ICL8038-based Oscillator

Posted on Feb 6, 2014

The circuit is a fairly easy design: It consists of the actual VCO (ICL8038 with supplement parts), the sine and triangle output stage (LT1210) and the CMOS-compatible output stage using the MOSFET driver chip ICL7667. The ICL8038 and all parts around on the lower half of the sheet make up the actual oscillator which is a modified design based on

ICL8038-based Oscillator
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one of the application examples in Intersil `s data sheet. There is a large 6-stage switch (S1) to select the major frequency and a logarithmic potentiometer (R2) for minor frequency selection. I discourage implementing the oscillator as shown in the above sheet because most of the other potentiometers turned out to be without significant enough effect on the output wave form to jusify their application. Furthermore, duty cycle adjustment will not keep a 50% ratio over all frequencies. The CD4030 on the left top is used as CMOS-logic signal preconditioning feeding the MOSFET driver IC ICL7667 as output stage for the complementary square wave output. The application of the two XOR gates has the advantage that it can supply a sqare wave and its complement without time offset between them (because CMOS has balanced raise and fall times). Use a bypass capacitor near the ICL7667 device as it can draw quite strong currents and is capable of driving into 50Ohm up to at least 10V resulting in rise/fall times of 30ns. So, I`m now entirely satisfied with the digital output. The industry-standard LM741 in combination with R11 is used to adjust the sine/triangle offset level. (Hint: You should probably use something better here - especially more output current cannot hurt. ) Since this oscillator is single-supply, it comes handy that you can change the "zero level" of the wave output; you will normally adjust that to half of the supply...

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