Signal processing circuit

Abstract

An integration type D/A and A/D converter having improved linearity and low power consumption. Logic circuits such as ECL counters consuming a major part of power of the D/A and A/D converters are realized through CMOS process. Current source circuits, current switch circuit and comparator circuit of the integration type A/D converter are realized in IC through bipolar process ensuring high accuracy and low noise. Logic parts such as counter is realized through CMOS process.

We claim: 
     
       1. A signal .[.porocessing.]. .Iadd.processing .Iaddend.circuit comprising: integrating means including a capacitor for integrating a constant current as a function of time;   a first circuit constituting pulse duration generating means for determining the integration time;   a second circuit including at least a current switch circuity for turning on and off the current supplied from current source means independence on said integration time;   said first and second circuits being implemented as integrated circuits separately in respective chips;   said first circuit being integrated by complementary MOS FET process on a same semiconductor substrate together with at least a digital signal processing circuit constituting error .Iadd.detection and .Iaddend.correction processing means for processing .[.a PCM.]. .Iadd.errors in a .Iaddend.signal .Iadd.being supplied thereto and outputting an error processed signal to said first circuit; .Iaddend.and   said second circuit being realized through bipolar process.   
     
     
       2. A signal processing circuit, comprising: integrating means including a capacitor for integrating a constant current as a function of time;   a first circuit constituting pulse duration generating means for determining the integration time;   a second circuit including at least a current switch circuitry for turning on and off the current supplied from current source means in dependence on said integration time;   said first and second circuits being implemented as integrated circuits separately in respective chips; and   said first circuit being integrated by complementary MOS FET process on a same semiconductor substrate integrally with a digital signal processing circuit which is constituted at least by multiplication means for multiplying .[.PCM.]. data and cumulative addition means for adding cumulatively the output of said multiplication means.   
     
     
       3. A signal processing circuit comprising: integrating means including a capacitor for integrating a constant current as a function of time;   a first circuit constituting pulse duration generating means for determining the integration time;   a second circuit including at least a current switch circuitry for turning on and off the current supplied from current source means in dependence on said integration time;   said first and second circuits being implemented as integrated circuits separately in respective chips; and   said first circuit being constituted by complementary MOS FETs while said second circuit being realized through bipolar process,   wherein said integrating means constitutes an A/D conveter for converting an analogue signal to a digital signal by discharging an analogue voltage charged in the capacitor with constant currents and counting a clock signal to determine the time .[.take.]. .Iadd.taken .Iaddend.for the charge of said capacitor to attain a predetermined value, said A/D conveter including a first circuitry constituting counting means for counting the integration time corresponding to said analogue voltage value with said clock signal, and at least a second circuit composed of a current switch circuitry for turning on and off the current of the current source means in accordance with the integration time, said first and second .[.circuities.]. .Iadd.circuitries .Iaddend.being implemented in the form of integrated circuits separately in respective chips, said first circuitry being realized through complementary MOS FET process, while said second circuitry being realized through bipolar process, and   wherein said first circuitry is integrated on a same semiconductor substrate together with at least a digital signal processing circuit constituting error .Iadd.detection and .Iaddend.correction processing means for processing .[.PCM.]. .Iadd.errors in .Iaddend.a signal .Iadd.being supplied thereto and outputting an error processed signal to said first circuit.Iaddend..   
     
     
       4. A signal processing circuit .[.according to claim 3, including.]. .Iadd.comprising: integrating means including a capacitor for integrating a constant current as a function of time;   a first circuit constituting pulse duration generating means for determining the integration time;   a second circuit including at least a current switch circuitry for turning on and off the current supplied from current source means in dependence on said integration time;   said first and second circuits being implemented as integrated circuits separately in respective chips; and   said first circuit being constituted by complementary MOS FETs while said second circuit being realized through bipolar process,   wherein said integrating means constitutes an A/D converter for converting an analogue signal to a digital signal by discharging an analogue voltage charged in the capacitor with constant currents and counting a clock signal to determine the time taken for the charge of said capacitor to attain a predetermined value, said A/D converter including a first circuitry constituting counting means for counting the integration time corresponding to said analogue voltage value with said clock signal, and at least a second circuit composed of a current switch circuitry for turning on and off the current of the current source means in accordance with the integration time, said first and second circuitries being implemented in the form of integrated circuits separately in respective chips, said first circuitry being realized through complementary MOS FET process, while said second circuitry being realized through bipolar process, and   wherein said first circuitry is integrated on a same semiconductor substrate together with at least a digital signal processing circuit constituting error detection and correction processing means for processing errors in a signal; and .Iaddend.   at least a first power supply means for supplying electric power to said error correcting means, and second power supply means for supplying electric power to said integration time counting means, to thereby suppress mutual interference between said integration time counting means and said error correcting means.   
     
     
       5. A signal processing circuit .[.according to claim 3,.]. .Iadd.comprising: integrating means including a capacitor for integrating a constant current as a function of time;   a first circuit constituting pulse duration generating means for determining the integration time;   a second circuit including at least a current switch circuitry for turning on and off the current supplied from current source means in dependence on said integration time;   said first and second circuits being implemented as integrated circuits separately in respective chips; and   said first circuit being constituted by complementary MOS FETs while said second circuit being realized through bipolar process,   wherein said integrating means constitutes an A/D converter for converting an analogue signal to a digital signal by discharging an analogue voltage charged in the capacitor with constant currents and counting a clock signal to determine the time taken for the charge of said capacitor to attain a predetermined value, said A/D converter including a first circuitry constituting counting means for counting the integration time corresponding to said analogue voltage value with said clock signal, and at least a second circuit composed of a current switch circuitry for turning on and off the current of the current source means in accordance with the integration time, said first and second circuitries being implemented in the form of integrated circuits separately in respective chips, said first circuitry being realized through complementary MOS FET process, while said second circuitry being realized through bipolar process, and   wherein said first circuitry is integrated on a same semiconductor substrate together with at least a digital signal processing circuit constituting error detection and correction processing means for processing errors in a signal; .Iaddend.   wherein the pulse duration signal generating means for generating a control signal for controlling current switch means for turning on and off the current to be integrated is provided with pulse duration adding means for providing a pulse duration of a predetermined time duration, to preset the minimum pulse duration generated by said pulse duration generating means not shorter than said predetermined time duration.   
     
     
       6. A signal processing circuit comprising: integrating means including a capacitor for integrating a constant current as a function of time;   a first circuit constituting pulse duration generating means for determining the integration time;   a second circuit including at least a current switch circuitry for turning on and off the current supplied from current source means in dependence on said integration time;   said first and second circuits being implemented as integrated circuits separately in respective chips; and   said first circuit being constituted by complementary MOS FETs while said second circuit being realized through bipolar process,   wherein siad integrating means constitutes an A/D converter for converting an analogue signal to a digital signal by discharging an analogue voltage charged in the capacitor with constant currents and counting a clock signal to determine the time .[.take.]. .Iadd.taken .Iaddend.for the charge of said capacitor to attain a predetermined value, said A/D converter including a first cirucitry constituting counting means for counting the integration time corresponding to said analogue voltage value with said clock signal, and at least a second .[.cirucit.]. .Iadd.circuit .Iaddend.composed of a current switch circuitry for turning on and off the current of the current source means in accordance with the integration time, said first and second circuitries being implemented in the form of integrated circuits separately in respective chips, said first .[.cirucitry.]. .Iadd.circuitry .Iaddend.being realized through complementary MOS FET process, while said second circuitry being realized through bipolar process, and   wherein said first cirucitry is integrated on a same semiconductor substrate integrally with a digital signal processing circuit which is constituted by multiplication means for multiplying output X resulting from the A/D conversion with a multiplier Y to perform operations given by P=X.Y and cumulative addition means for adding cumulatively the output P of said multiplication means.   
     
     
       7. A signal processing circuit according to claim 6, including first power supply means for supplying electric power to said multiplication means and said cumulative addition means, and second power supply means for supplying electric power to said integration time counting means, to thereby supress mutual interference between said multiplication means and cumulative addition means on one hand and said integration time counting means on the other hand. 
     
     
       8. A signal processing circuit according to claim 6, wherein the pulse duration signal generating means for generating a control signal for controlling current switch means for turning on and off the current to be integrated is provided with pulse duration adding means for providing a pulse duration of a predetermined time duration, to preset the minimum pulse duration generated by said pulse duration generating means not shorter than said predetermined time duration. 
     
     
       9. A signal processing circuit comprising: integrating means including a capacitor for integrating a constant current as a function of time;   a first circuit constituting pulse duration generating means for determining the integration time;   a second circuit including at least a current switch circuitry for turning on and off the current supplied from current source means in dependence on said integration time;   said first and second circuits being implemented as integrated circuits separately in respective chips; and   said first circuit being constituted by complementary MOS FETs while said second circuit being realized through bipolar process,   wherein said integrating means constitutes an A/D converter for converting an analogue signal to a digital signal by discharging an analogue voltage charged in the capacitor with constant currents and counting a clock signal to determine the time .[.take.]. .Iadd.taken .Iaddend.for the charge of said capacitor to attain a predetermined value, said A/D converter including a first circuitry constituting counting means for counting the integration time corresponding to said analogue voltage value with said clock signal, and at least a second circuit composed of a current switch circuitry for turning on and off the current of the current source means in accordance with the integration time, said first and second circuitries being implemented in the form of integrated circuits separately in respective chips, said first circuitry being realized through complementary MOS FET process, while said second circuitry being realized through bipolar process,   said second circuitry including at least a plurality of current sources, a plurality of current switches and a plurality of comparators, wherein reference levels of said comparators being varied in accordance with a total sum of delay time involved in signal transmission from said first circuitry to said second circuitry and delay time involved in signal transmission from said second circuitry to said first circuitry. .Iadd.   
     
     
       10.  A signal processing circuit comprising: integrating means for integrating a constant current source as a function of time;   a first circuit constituting pulse duration generating means for determining the integration time;   a second circuit for turning on and off the current supplied from current source means in dependence on said integration time;   said first and second circuits being implemented as integrated circuits separately in respective chips;   said first circuit and at least a digital signal processing circuit being realized by complementary MOSFET process, said digital signal processing circuit is provided for processing a signal;   said second circuit being realized through bipolar process;   wherein said integrating means includes a capacitor for integrating said constant current;   wherein said second circuit includes at least a current switch circuitry for turning on and off the current supplied from current source means;   wherein said first circuit and said digital signal processing circuit are integrated on a same semiconductor substrate;   wherein said digital signal processing circuit includes an error correction processing means for processing errors in said signal;   said integrating means constitutes a converter for converting a first signal to a second signal by integrating the constant current source as a function of time, said converter including said first circuit constituting pulse duration generating means for determining the integration time and said second circuit for turning on and off the current supplied from said current source means based on said integration time;   wherein said convertor is a digital to analog (D/A) convertor for converting a digital signal to an analog signal. .Iaddend. .Iadd.   
     
     
       11.  A signal processing circuit according to claim 10, further including first power supply means for supplying electric power to said error correcting means and second power supply means for supplying electric power to said pulse duration generating means, to thereby suppress mutual interference between said pulse duration generating means and said error correcting means. .Iaddend. .Iadd.12. A signal processing circuit according to claim 10, further comprising: multiplication means for multiplying the output X of at least said error correcting means with a multiplicator Y to perform an operation given by P=X×Y, and cumulative addition means for adding cumulatively the output P of said multiplication means, wherein said pulse duration generating means generates a pulse having a pulse duration which is in proportion to the magnitude of the output of said cumulative addition means, said multiplication means and said cumulative addition means being implemented on the same semiconductor substrate integrally with said pulse duration generating means, said constant current source means being controlled by the output signal of said pulse duration generating means for deriving an analog signal by integrating the current of said constant current source means through said integrating means. .Iaddend. .Iadd.13. A signal processing circuit according to claim 12, further comprising:   first power supply means for providing a power source to said multiplication means and said cumulative addition means, and second power supply means for providing a power source to said pulse duration generating means to thereby suppress mutual interference between said multiplication means and said cumulative addition means on one hand, and said pulse duration signal generating means on the other hand. .Iaddend.   
     
     
        .Iadd.14.  A signal processing circuit comprising: integrating means for integrating a constant current source as a function of time;   a first circuit constituting pulse duration generating means for determining the integration time;   a second circuit for turning on and off the current supplied from current source means in dependence on said integration time;   said first and second circuits being implemented as integrated circuits separately in respective chips;   said first circuit and at least a digital signal processing circuit being realized by complementary MOSFET process, said digital signal processing circuit is provided for processing a signal;   said second circuit being realized through bipolar process;   wherein said integrating means includes a capacitor for integrating said constant current;   wherein said second circuit includes at least a current switch circuitry for turning on and off the current supplied from current source means;   wherein said first circuit and said digital signal processing circuit are integrated on a same semiconductor substrate;   wherein said digital signal processing circuit includes an error correction processing means for processing errors in said signal;   said integrating means constitutes a converter for converting a first signal to a second signal by integrating the constant current source as a function of time, said converter including said first circuit constituting pulse duration generating means for determining the integration time and said second circuit for turning on and off the current supplied from said current source means based on said integration time;   wherein said convertor is an analog to digital (A/D) convertor for converting an analog signal to a digital signal;   said pulse duration generating means for generating a control signal for controlling said current switch circuitry and is provided with pulse duration adding means for providing a pulse duration of a predetermined time duration to thereby preset the minimum pulse duration generated by said pulse duration generating means not shorter than said predetermined   
     
     
        time. .Iaddend. .Iadd.15.  A signal processing circuit comprising: integrating means for integrating a constant current source as a function of time;   a first circuit constituting pulse duration generating means for determining the integration time;   a second circuit for turning on and off the current supplied from current source means in dependence on said integration time;   said first and second circuits being implemented as integrated circuits separately in respective chips;   said first circuit and at least a digital signal processing circuit being realized by complementary MOSFET process, said digital signal processing circuit is provided for processing a signal;   said second circuit being realized through bipolar process;   wherein said integrating means includes a capacitor for integrating said constant current;   wherein said second circuit includes at least a current switch circuitry for turning on and off the current supplied from current source means;   wherein said first circuit and said digital signal processing circuit are integrated on a same semiconductor substrate;   wherein said digital signal processing circuit includes an error correction processing means for processing errors in said signal;   said integrating means constitutes a converter for converting a first signal to a second signal by integrating the constant current source as a function of time, said converter including said first circuit constituting pulse duration generating means for determining the integration time and said second circuit for turning on and off the current supplied from said current source means based on said integration time;   wherein said convertor is an analog to digital (A/D) convertor for converting an analog signal to a digital signal;   said first circuit is integrated on the same semiconductor substrate integrally with a digital signal processing circuit which is constituted by multiplication means for multiplying an output X resulting from the A/D conversion with a multiplicator Y to perform an operation given by P=X×Y and cumulative addition means for adding cumulatively the   
     
     
        output P of said multiplication means. .Iaddend. .Iadd.16.  A signal processing circuit according to claim 15, further comprising: first power supply means for supplying electric power to said multiplication means and said cumulative addition means and second power supply means for supplying electric power to said pulse duration generating means to thereby suppress mutual interference between said multiplication means and said cumulative addition means on one hand and said pulse duration generating means on the other hand. .Iaddend.   
     
     
        .Iadd.     A signal processing circuit comprising: integrating means for integrating a constant current source as a function of time;   a first circuit constituting pulse duration generating means for determining the integration time;   a second circuit for turning on and off the current supplied from current source means in dependence on said integration time;   said first and second circuits being implemented as integrated circuits separately in respective chips;   said first circuit and at least a digital signal processing circuit being realized by complementary MOSFET process, said digital signal processing circuit is provided for processing a signal;   said second circuit being realized through bipolar process;   wherein said integrating means includes a capacitor for integrating said constant current;   wherein said second circuit includes at least a current switch circuitry for turning on and off the current supplied from current source means;   wherein said first circuit and said digital signal processing circuit are integrated on a same semiconductor substrate;   wherein said digital signal processing circuit includes an error correction processing means for processing errors in said signal;   said integrating means constitutes a converter for converting a first signal to a second signal by integrating the constant current source as a function of time, said converter including said first circuit constituting pulse duration generating means for determining the integration time and said second circuit for turning on and off the current supplied from said current source means based on said integration time;   wherein said convertor is an analog to digital (A/D) convertor for converting an analog signal to a digital signal;   said pulse duration signal generating means generates a control signal for controlling said current switch circuitry and is provided with pulse duration adding means for providing a pulse duration of a predetermined time duration to thereby preset the minimum pulse duration generated by said pulse duration generating means not shorter than said predetermined   
     
     
        time duration. .Iaddend. .Iadd.18.  A signal processing circuit comprising: integrating means for integrating a constant current source as a function of time;   a first circuit constituting pulse duration generating means for determining the integration time;   a second circuit for turning on and off the current supplied from current source means in dependence on said integration time;   said first and second circuits being implemented as integrated circuits separately in respective chips;   said first circuit and at least a digital signal processing circuit being realized by complementary MOSFET process, said digital signal processing circuit is provided for processing a signal;   said second circuit being realized through bipolar process;   wherein said integrating means includes a capacitor for integrating said constant current;   wherein said second circuit includes at least a current switch circuitry for turning on and off the current supplied from current source means;   wherein said first circuit and said digital signal processing circuit are integrated on a same semiconductor substrate;   wherein said digital signal processing circuit includes an error correction processing means for processing errors in said signal;   said integrating means constitutes a converter for converting a first signal to a second signal by integrating the constant current source as a function of time, said converter including said first circuit constituting pulse duration generating means for determining the integration time and said second circuit or turning on and off the current supplied from said current source means based on said integration time;   wherein said convertor is an analog to digital (A/D) convertor for converting an analog signal to a digital signal;   said second circuit includes at least said current source means, said current switch and a plurality of comparators, wherein reference levels of said comparators being varied in accordance with a total sum of delayed time involved in signal transmission from said first circuit to said second circuit and delayed time involved in signal transmission from said   
     
     
        second circuit to said first circuit. .Iaddend. .Iadd.19.  A signal processing circuit integrating means for integrating a constant current source as a function of time; a first circuit constituting pulse duration generating means for determining the integration time;   a second circuit for turning on and off the current supplied from current source means in dependence on said integration time;   said first and second circuits being implemented as integrated circuits separately in respective chips; and   said first circuit being realized by complementary MOSFET process while said second circuit being realized through bi-polar process;   said integrating means constitutes a converter for converting a first signal to a second signal by integrating the constant current as a function of time, said converter including said first circuit constituting pulse duration generating means for determining the integration time and said second circuit for turning on and off the current supplied from said current source means based on said integration time;   wherein said convertor constitutes a digital to analog (D/A)convertor for   
     
     
        converting a digital signal to an analog signal. .Iaddend. .Iadd.20.  A signal processing circuit comprising; integrating means for integrating a constant current source as a function of time;   a first circuit constituting pulse duration generating means for determining the integration time;   a second circuit for turning on and off the current supplied from current source means in dependence on said integration time;   said first and second circuits being implemented as integrated circuits separately in respective chips; and   said first circuit being realized by complementary MOSFET process while said second circuit being realized through bi-polar process;   said integrating means constitutes a converter for converting a first signal to a second signal by integrating the constant current as a function of time, said converter including said first circuit constituting pulse duration generating means for determining the integration time and said second circuit for turning on and off the current supplied from said current source means based on said integration time;   said integrating means includes a capacitor for integrating said constant current;   wherein said second circuit includes at least a current switch circuitry for turning on and off current supplied form current source means;   wherein said convertor constitutes a digital to analog (D/A) convertor for   
     
     
        converting a digital signal to an analog signal. .Iaddend. .Iadd.21.  A signal processing circuit according to claim 20, wherein said first circuit is implemented on a same semiconductor substrate integrally with at least a digital signal processing circuit constituting error correcting means for reproducing a signal. .Iaddend. .Iadd.22. A signal processing circuit according to claim 21, further comprising: first power supply means for supplying electric power to said error correcting means and second power supply means for supplying electric power to said pulse duration generating means, to thereby suppress mutual interference between said pulse duration generating means and said error   
     
     
        correcting means. .Iaddend. .Iadd.23.  A signal processing circuit according to claim 21, further comprising: multiplication means for multiplying the output X of at least said error correcting means with a multiplicator Y to perform an operation given by P=X×Y, and cumulative addition means for adding cumulatively the output P of said multiplication means, wherein said pulse duration generating means generates a pulse having a pulse duration which is in proportion to the magnitude of the output of said cumulative means, said multiplication and said cumulative addition means being implemented on said semiconductor substrate generally with said pulse duration generating means, said constant current source means being controlled by the output signal of said pulse duration for deriving an analog signal by integrating the current of said current source means through said integrating means. .Iaddend. .Iadd.24. A signal processing circuit according to claim 23, further comprising:   first power supply means for providing a power supply source to said multiplication means and said cumulative addition means, second power supply means for providing a power source to said pulse duration generating means to thereby suppress mutual interference between said multiplication means and said cumulative addition means on one hand, and said second pulse duration generating means on the other hand. .Iaddend.   
     
     
        .Iadd.25.  A signal processing circuit comprising; integrating means for integrating a constant current source as a function of time;   a first circuit constituting pulse duration generating means for determining the integration time;   a second circuit for turning on and off the current supplied from current source means in dependence on said integration time;   said first and second circuits being implemented as integrated circuits separately in respective chips; and   said first circuit being realized by complementary MOSFET process while said second circuit being realized through bi-polar process;   said integrating means constitutes a converter for converting a first signal to a second signal by integrating the constant current as a function of time, said converter including said first circuit constituting pulse duration generating means for determining the integration time and said second circuit for turning on and off the current supplied from said current source means based on said integration time;   said integrating means includes a capacitor for integrating said constant current;   wherein said second circuit includes at least a current switch circuitry for turning on and off current supplied from current source means;   wherein said convertor constitutes an analog to digital (A/D) convertor for converting an analog signal to a digital signal;   wherein said first circuit is implemented on a same semiconductor substrate integrally with at least a digital signal processing circuit constituting   
     
     
        error correcting means for reproducing a signal. .Iaddend. .Iadd.26.  A signal processing circuit according to claim 25, further comprising: first power supply means for supply electric power to said error correcting means and second power supply means for supply electric power to said pulse duration generating means, to thereby suppress mutual interference between said pulse duration generating means and said error correcting   
     
     
        means. .Iaddend. .Iadd.27.  A signal processing circuit comprising; integrating means for integrating a constant current source as a function of time;   a first circuit constituting pulse duration generating means for determining the integration time;   a second circuit for turning on and off the current supplied from current source means in dependence on said integration time;   said first and second circuits being implemented as integrated circuits separately in respective chips; and   said first circuit being realized by complementary MOSFET process while said second circuit being realized through bi-polar process;   said integrating means constitutes a converter for converting a first signal to a second signal by integrating the constant current as a function of time, said converter including said first circuit constituting pulse duration generating means for determining the integration time and said second circuit for turning on and off the current supplied from said current source means based on said integration time;   said integrating means includes a capacitor for integrating said constant current;   wherein said second circuit includes at least a current switch circuitry for turning on and off current supplied from current source means;   wherein said convertor constitutes an analog to digital (A/D) convertor for converting an analog signal to a digital signal;   said pulse duration generating means generates a control signal for controlling said current switch circuitry and is provided with pulse duration adding means for providing a pulse duration of a predetermined time duration, to thereby preset the minimum pulse duration generation by said pulse duration generated means not shorter than said predetermined   
     
     
        time duration. .Iaddend. .Iadd.28.  A signal processing circuit comprising; integrating means for integrating a constant current source as a function of time;   a first circuit constituting pulse duration generating means for determining the integration time;   a second circuit for turning on and off the current supplied from current source means in dependence on said integration time;   said first and second circuits being implemented as integrated circuits separately in respective chips; and   said first circuit being realized by complementary MOSFET process while said second circuit being realized through bi-polar process;   said integrating means constitutes a converter for converting a first signal to a second signal by integrating the constant current as a function of time, said converter including said first circuit constituting pulse duration generating means for determining the integration time and said second circuit for turning on and off the current supplied from said current source means based on said integration time;   said integrating means includes a capacitor for integrating said constant current;   wherein said second circuit includes at least a current switch circuitry for turning on and off current supplied from current source means;   wherein said convertor constitutes an analog to digital (A/D) convertor for converting an analog signal to a digital signal;   said first circuit is integrated on the same semiconductor substrate integrally with a digital signal processing circuit which is constituted by multiplication means for multiplying an output X resulting from the A/D conversion with a multiplicator Y to perform an operation given by P=X×Y and cumulative addition means for adding cumulatively the   
     
     
        output P of said multiplication mean. .Iaddend. .Iadd.29.  A signal processing circuit according to claim 28, further comprising: first power supply means for supplying electric power to said multiplication means and said cumulative addition means and second power supply means for supplying electric power to said pulse duration generating means to thereby suppress mutual interference between said multiplication means and said cumulative addition means on one hand and said pulse duration generating means on the other hand. .Iaddend. .Iadd.30. A signal processing circuit according to claim 25, wherein:   said pulse duration signal generating means generates a control signal for controlling said current switch circuitry and is provided with pulse duration adding means for providing a pulse duration of a predetermined duration to thereby preset the minimum pulse duration generated by said pulse duration generating means not shorter than said predetermined time   
     
     
        duration. .Iaddend. .Iadd.31.  A signal processing circuit comprising; integrating means for integrating a constant current source as a function of time;   a first circuit constituting pulse duration generating means for determining the integration time;   a second circuit for turning on and off the current supplied from current source means in dependence on said integration time;   said first and second circuits being implemented as integrated circuits separately in respective chips; and   said first circuit being realized by complementary MOSFET process while said second circuit being realized through bi-polar process;   said integrating means constitutes a converter for converting a first signal to a second signal by integrating the constant current as a function of time, said converter including said first circuit constituting pulse duration generating means for determining the integration time and said second circuit for turning on and off the current supplied from said current source means based on said integration time;   said integrating means includes a capacitor for integrating said constant current;   wherein said second circuit includes at least a current switch circuitry for turning on and off current supplied from current source means;   wherein said convertor constitutes an analog to digital (A/D) convertor for converting an analog signal to a digital signal;   said second circuit includes at least said current source means, said at least a current switch circuitry and a plurality of comparators, wherein reference levels of said comparators being varied in accordance with a total sum of delayed time involved in signal transmission from said first circuit to said second circuit and delayed time involved in signal transmission from said second circuit to said first circuit.