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A tone generator system for an electronic organ which is capable of being fabricated into an LSI structure and receives a saw-tooth wave or staircase wave as an input thereto comprises a frequency divider for the saw-tooth wave or staircase wave including a ladder resistor network and a complementary MOS FET devices, an analog switch having a wide dynamic range and a high linearity in input-output transfer characteristic constructed by MOS FET devices to serve as an indirect keying means, a sustain means including a novel structure of a variable impedance element which is constructed to control a channel current in a MOS FET device by varying the potential distribution in the source region, and an impedance coverter constructed by complementary MOS FET devices and free from a D.C. level shift. With the above arrangement a tone generator system of high quality for an electronic organ is provided.

The present invention is an integrated circuit for an electronic musical instrument comprising: a plurality of frequency divider chains receiving a plurality of input signals for dividing the frequencies of the input signals one after another and corresponding to a plurality of series of adjacent notes which are chromatically arranged in turn in a twelve-tone of a musical scale, respectively; keyer-gates for switching on and off the input signals and output signals of the frequency dividers of the frequency divider chains respectively; and adding means for adding at least two output signals of the keyer-gates which correspond to the adjacent notes chromatically arranged to each other, so as to produce output tone signals therefrom, respectively.

PURPOSE:To make the integration of musical tone generating circuits higher in efficiency by providing capacity groups which store analog musical tone amplitude values at the scanning of keyboard switches and envelope controlling capacity groups. CONSTITUTION:Transistors Q11, Q12 of circuit blocks 101 thru 161 are controlled by the matrix signals corresponding to key touching through scanning of keyboard switch blocks, whereby the analog musical tone amplitude values applied as the gate capacities of MOS type FETs Q13, Q14 and Q16, Q17 to the blocks 101 thru 161 are stored and the musical tone signals are generated. On the other hand, the evelope of the musical tone signals is suppressed by charging and discharging of the block 200 provided with capacity element groups K201, K202... of the storage periods sufficiently longer than keyboard scan periods such as bucket brigades, charge transfer elements, etc. connecting to the transistors Q201, Q202... of the impedance Z1 controlled by the outputs of the blocks 101 thru 161. Hence, if there is no need for envelope depending upon musical instruments, the block 200 may be saved, thus the efficient large scale integration of the musical tone forming circuits may be achieved.