Electronic musical instrument having portamento property

Abstract

In a electronic musical instrument wherein a portamento is played by supplying the pitch voltage corresponding to a subsequently depressed key to a capacitor holding the pitch voltage corresponding to a previously depressed key, the charge and discharge currents of the capacitor corresponding to the difference between the two pitch voltages are controlled to vary exponentially thus changing exponentially the capacitor terminal voltage. The terminal voltage of the capacitor is applied to drive a voltage controlled oscillator to vary its oscillation frequency. To vary exponentially the terminal voltage of the capacitor, a mutual conductance converter is connected between the capacitor and a keyboard section and the output current from the mutual conductance converter is controlled by a control signal corresponding to the terminal voltage of the capacitor.

What is claimed is: 
     
       1. In an electronic musical instrument including a capacitor which is charged with a pitch voltage to hold the same, and a voltage controlled type oscillator which is controlled by the terminal voltage of said capacitor for playing a portamento, the improvement which comprises a first mutual conductance converter responsive to an input voltage signal to produce a current signal for varying said capacitor terminal voltage, means for supplying the current signal of said mutual conductance converter to said capacitor, means for detecting said capacitor terminal voltage to produce a control voltage signal corresponding to said capacitor terminal voltage, means coupled to said mutual conductance converter and said detecting means for controlling the current signal of said mutual conductance converter in accordance with said control voltage signal so that said current signal is substantially directly proportional to said capacitor terminal voltage thereby causing said capacitor terminal voltage to vary exponentially with respect to time both in ascending and descending characteristics, and a comparator responsive to said pitch voltage and said capacitor terminal voltage for delivering to said mutual conductance converter an output voltage signal as said input voltage signal to said converter when said capacitor terminal voltage is in a predetermined relation in magnitude to said pitch voltage, said voltage controlled type oscillator having a substantially linear input-output characteristic thereby producing a tone signal having a frequency varying exponentially with respect to time in said both characteristics. 
     
     
       2. The electronic musical instrument according to claim 1 wherein said mutual conductance converter is of a current controlled type. 
     
     
       3. The electronic musical instrument according to claim 2 wherein said mutual conductance converter comprises first and second transistors with their emitter electrodes commonly connected so as to constitute a differential amplifier, first and second current mirror circuits for deriving out a current variation corresponding to the collector currents of said transistors, a circuit for deriving out the difference between the output currents from said first and second current mirror circuits as said current signal, and a circuit for applying a control current corresponding to said control voltage signal to the emitter electrodes of said first and second transistors. 
     
     
       4. The electronic musical instrument according to claim 4 wherein said current signal control means is connected to supply to said mutual conductance converter a control current corresponding to the control voltage signal of said detecting means which is proportional to the terminal voltage of said capacitor. 
     
     
       5. The electronic musical instrument according to claim 5 wherein said current signal control means comprises a bipolar transistor with its base electrode supplied with a fixed bias potential, the emitter electrode supplied with the output control voltage signal from said detecting means, and the collector electrode connected to supply a collector current proportional to said control voltage signal to said mutual conductance converter. 
     
     
       6. The electronic musical instrument according to claim 5 wherein said current signal control means further comprises a variable resistor connected between said detecting means and the emitter electrode of said bipolar transistor to control a tempo of the portamento. 
     
     
       7. The electronic musical instrument according to claim 4 wherein said current signal control means comprises a bipolar transistor and an amplifier, and wherein the control voltage signal from said detecting means is applied to the base electrode of said bipolar transistor via said amplifier, the emitter electrode of said transistor is connected to a source through a load, and the collector electrode is connected to apply the collector current corresponding to the control voltage signal to said mutual conductance converter. 
     
     
       8. The electronic musical instrument according to claim 1 wherein said detecting means includes a buffer circuit having a high input impedance and a low output impedance, the terminal voltage of said capacitor is applied to the input of said buffer circuit and the output from said buffer circuit, is applied to said current signal control means. 
     
     
       9. The electronic musical instrument according to claim 8 wherein said buffer circuit comprises a source follower amplifier including a field effect transistor. 
     
     
       10. The electronic musical instrument according to claim 1 which further comprises a voltage dividing circuit connected between said comparator and said mutual conductance converter. 
     
     
       11. The electronic musical instrument according to claim 1 wherein said current signal control means comprises a second mutual conductance converter connected to receive the control voltage signal from said detecting means, a current controlling circuit for supplying to said second mutual conductance converter a control signal corresponding to a portamento tempo control voltage, and means for applying to said first mutual conductance converter the output from said second mutual conductance converter to act as the control signal for the first mutual conductance converter thereby controlling the output current signal of the first mutual conductance converter in accordance with said tempo control voltage. .Iadd. 
     
     
       12.  In an electronic musical instrument including a capacitor which is charged with a pitch voltage signal to hold the same, and a voltage controlled type oscillator which is controlled by the terminal voltage of said capacitor for playing a portamento, the improvement which comprises means responsive to said pitch voltage signal for generating a current signal to vary said capacitor terminal voltage exponentially through charging and discharging said capacitor in accordance with said current signal, means for detecting said capacitor terminal voltage to produce a control signal, means coupled to said current signal generating means for controlling the same in response to said control signal so that said current signal increases and decreases in magnitude when said capacitor terminal voltage increases and decreases exponentially, respectively, and means for causing said current signal generating means to cease from generating said current when said capacitor terminal voltage is in a predetermined relation in magnitude to said pitch voltage signal. .Iaddend.