Multiplier, divider and wattmeter using a switching circuit and a pulse-width and frequency modulator

Abstract

In the switching circuit, the output signal from a high-gain differential amplifier is caused to reverse polarity by means of the switching of a pair of field-effect transistors. A resistor is connected in series with the inverting lead of the differential amplifier, and a signal source is connected to the resistor at an input terminal. The field-effect transistors are used to connect the non-inverting lead of the differential amplifier alternately between the input terminal and ground. This causes the amplifier output to reverse polarity, and thus provides a very accurate, low-offset means of switching the output of the amplifier. The switching circuit is used in a modulator which permits output pulses to be modulated in width and/or frequency. The reversible output signals of the switching circuit are added to the modulating input signal and the sum is integrated. A level detector changes the polarity of its output voltage whenever the output of the integrator reaches either of two fixed levels. The output of the level detector is used to drive the field-effect transistors to control the switching of the output of the differential amplifier. Such a pulse-width modulator is used to drive a pulse-height modulator so as to form a multiplier. The multiplier can be used to great advantage as a wattmeter by supplying load current and voltage signals to the pulse-width and pulse-height modulators so as to multiply the load current and voltage by one another. The same device can be used as a divider by holding either one input to the pulse-width modulator or the input to the pulse-height modulator constant, while allowing the other of those inputs to be variable and the input to the switching circuit to be the other variable. .Iadd.

I claim: 
     
       1. A multiplier device comprising a pulse-width modulator controlled by a first input signal, and a pulse height modulator controlled by a second input signal and connected to said pulse-width modulator, said pulse-width modulator comprising source means for producing an output signal alternating between two levels in response to input switching signals, means for modifying at least one of said levels in response to a modulating signal, integrator means for integrating the output of said source means so modified, said source means including a switching device, said device including a high-gain differential amplifier having first and second input terminals, an impedance connected between the first of said input terminals and a third terminal for receiving an input signal, and gating means for connecting the second of said input terminals alternately between said third terminal and a fourth terminal for receiving a signal of a magnitude lower than the input signal applied to said third terminal, level detector means for detecting the output of said integrator means and producing an output signal change whenever the integrator output reaches either of two different pre-determined levels, and means for transmitting the output of said level detector means to said source means as input gating signals to said source means. 
     
     
       2. A multiplier as in claim 1 including a smoothing circuit for the output of said pulse-height modulator. 
     
     
       3. A wattmeter including a multiplier as in claim 1 with means for receiving inputs proportional to the load voltage and the load current of the power being measured. 
     
     
       4. A device as in claim 1 in which said switching means includes a pair of field effect transistors, one connected between said second and third terminals, and the other connected between said second and fourth terminals. 
     
     
       5. A device as in claim 1 in which said differential amplifier is an operational amplifier with a feed-back impedance connected between its output terminal and said first input terminal. 
     
     
       6. A device as in claim 1 in which said first terminal is an inverting terminal, and said second terminal is a non-inverting terminal. 
     
     
       7. A device as in claim 4 in which one of said transistors is of the P-channel type, and the other is of the N-channel type, a common connection to the gate leads of the transistors, the output of said level detector means being connected to said common connection. 
     
     
       8. A device as in claim 4 in which said transistors are of the same channel type, means connecting the output of said level detector means directly to the gate lead of one of said transistors, and an inverter connecting said output of said level detector means to the gate lead of the other transistor. 
     
     
       9. A device as in claim 1 in which said impedance is a resistor. 
     
     
       10. A device as in claim 1 in which said fourth terminal is common to the input and output of said source means. 
     
     
       11. A mathematical circuit device comprising a pulse-width modulator controlled by a first input signal, and a pulse height modulator controlled by a second input signal and connected to said pulse-width modulator, said pulse-width modulator including a circuit device for producing an output signal alternating between two levels in response to input switching signals, said circuit device including a high-gain differential amplifier having two input terminals and an output terminal, and means for reversing the polarity of the output signal on said output terminal in response to a change in polarity of the difference between the input signals on said input terminals, an impedance connected at one end to a first one of said input terminals and at the other end to a third signal-receiving terminal, a fourth terminal for receiving a reference signal, and switching means for connecting the second of said input terminals alternately to said third terminal and said fourth terminal, integrator means for integrating said output signal, level detector means for detecting the output of said integrator means and producing an output signal change whenever the integrator output reaches either of two different pre-determined levels, and means for transmitting the output of said level detector means as input gating signals to said circuit device. 
     
     
       12. A device as in claim 11 including a smoothing circuit for the output of said pulse-height modulator. 
     
     
       13. A wattmeter including a device as in claim 11 with means for receiving inputs proportional to the load voltage and the load current of the power being measured. 
     
     
       14. A device as in claim 11 in which said differential amplifier includes a summing circuit, an inverter connected between one of said input terminals and said summing circuit, said other input terminal being connected to deliver an uninverted input signal to said summing circuit, a signal amplifier connected to receive the output of said summing circuit, and a feedback impedance connected between said one input terminal and the output of said signal amplifier. 
     
     
       15. A device as in claim 11 in which said differential amplifier is an integrated operational amplifier and said feed-back impedance is an external resistor, the first-named impedance is a resistor, said switching means comprises a first field-effect transistor with its source-drain path connected between said second and third terminals, a second field-effect transistor with its source-drain path connected between said second terminal and ground, said transmitting means comprising means for connecting the output of said level detector means to the gate leads of said transistors and turning one of said transistors on while turning the other off. 
     
     
       16. A device as in claim 1 in which the frequency of the output of said level detector means is at least 100 times the frequency of said modulating signal. 
     
     
       17. A device as in claim 1 in which said levels of said level detector means are fixed and independent from said modulating input signal. 
     
     
       18. A device as in claim 1 in which said level detector means comprises an operational amplifier having inverting and non-inverting input terminals, the integrator output being connected to said inverting terminal, a bias impedance connected to said non-inverting terminal, and a positive feed-back impedance connected between said non-inverting terminal and the output of said operational amplifier. 
     
     
       19. A device as in claim 1 including a node at the output of said source means and the input of said integrator means, and means for conducting said modulating input signal into said node. 
     
     
       20. A device as in claim 1 including means for changing at least one of said levels of said level detector means in response to another modulating input signal, thereby changing the frequency of the output of said level detector as a function of said other modulating input signal. 
     
     
       21. A device as in claim 11 in which said level detector means includes an operational amplifier having inverting and non-inverting input terminals, the integrator output being connected to said inverting terminal, a bias resistor connected to the non-inverting terminal of said operational amplifier, and a feed-back resistor connected between the non-inverting terminal and the output of said operational amplifier. 
     
     
       22. An electrical device comprising, in combination, an integrator, level sense means responsive to the output of said integrator for producing a first signal of alternating polarity in which each polarity reversal occurs when said integrator output reaches one of two different signal levels, means for conducting said first alternating signal to the input of said integrator, first modulating means for changing the magnitude of said first signal in accordance with a first input variable X, second modulating means for changing the magnitude of said signal in accordance with a second input variable Y and thus forming a second signal, and means for controlling the separation between said different signal levels in accordance with said second signal. 
     
     
       23. A device as in claim 22 in which at least one of said first and second modulating means comprises a circuit device for producing an output signal alternating between two levels in response to input switching signals, said circuit device including a high-gain differential amplifier having two input terminals and an output terminal, and means for reversing the polarity of the output signal on said output terminal in response to a change in polarity of the difference between the input signals on said input terminals, an impedance connected at one end to a first one of said input terminals and at the other end to a third signal-receiving terminal, a fourth terminal for receiving an input variable signal, and switching means for connecting the second of said input terminals alternately to said third terminal and said fourth terminal. 
     
     
       24. A device as in claim 22 in which said level sensor means comprises an operational amplifier having inverting and non-inverting input terminals, the integrator output being connected to said inverting terminal, a bias impedance connected to said non-inverting terminal, and means for conducting said second signal to said non-inverting terminal.