Abstract: A CMOS input level shifting circuit includes a temperature-compensating N-channel field effect transistor structure wherein a resistance in series with the source region includes an extension of a lightly doped P-type region in which the source and drain regions are diffused. This structure produces a temperature-compensating variation in the drain current proportional to the square of the series resistance without requiring modification of standard processes for manufacturing CMOS integrated circuits. The relatively large, temperature-dependent variation of the series resistance produces a corresponding temperature-dependent variation in the drain current that effectively temperature-compensates the switching point of the CMOS input level shifting circuit.

Abstract: In a method of electrically altering the characteristics of a semiconductor device, a lateral polysilicon zener diode's zener knee voltage may be shifted either to a higher or lower voltage. An electrical potential may be applied in the forward direction to shift the zener knee to a higher voltage level. An electrical potential may be applied in the reverse bias direction to shift the zener knee to a lower voltage. In the limit, the zener may be changed into a forward diode of reverse polarity with respect to the original zener. The electrical potential used should be of appropriate magnitude to melt the polysilicon without damage to the zener's terminals. This induces migration of the impurities causing a rediffusion of impurities thereby altering the characteristics of the diode. This method may be used to program a PROM by either converting the zener to a diode or not to program each binary bit.

Abstract: The accuracy of a required tone set, digitally synthesized by a microprocessor, is improved beyond the theoretical limit of the microprocessor circuitry by producing each tone at a frequency which is a sub-multiple of the desired frequency, then multiplying to provide the desired frequency. With the addition of a multiplier such as a doubler, a better choice of oscillator frequency becomes possible which further increases the tone frequency accuracy. The microprocessor can also reduce the start up time and the time between tones, eliminating delays in transmitting a series of coded tones.