Problems with 74HC(T)xxxx and CMOS4xxx IC 'linear' circuits. The following reproducible problems were found in several popular 'analog' applications of CMOS gate based circuits. The circuits are tried-and-true 'old' circuits from the 1980s and 1970s, as published in datasheets and application notes from various name silicon makers. 1 - inverter-with-feedback-resistor does not work or oscillates uncontrollably. Occurs with 74HC(T)xxx circuits, any. Using any feedback resistor over a simple inverter in a 74HC(T) circuit=20 causes the gate to oscillate at over 10 MHz. The resistor value does not matter. The oscillation also occurs if an external precise bias source is used to bias the input, without using a feedback resistor. Source impedances tried ranged from 1 ohm to 10Megohms. Consequences: - It is not possible to build low frequecy Xtal oscillators=20 using 74HC(T)xxxx gates. Example: 32767kHz osc on 74HC(T)4060 will not work, it oscillates at several MHz. Manipulating the usual Pierce oscillator part values around the xtal does not help. This does not appear anywhere in the datasheet. 2 - CMOS oscillators built as above with gate-and-feedback resistor stop working when the supply voltage is taken up above 5V. Example: CD4060 with 32768kHz Xtal using datasheet Pierce oscillator values (2.2kohms, 2x33pF, 2M2 feedback), works fine at 5V but stops working at about 7V supply and is impossible to start at 12V. My assumption is, that there is some 'new' 'feature' caused by die shrinks which increases leakage at the input and/or lowers output impedance somehow, or that gain decreases with voltage somehow in the 'deadband' dc bias region. In all cases I tried several Xtals (3 makes), and several ICs (2 or 3 makes each). All ICs were new (datecode >2007). I did not try old old parts (CD4060 etc) beucause I know they work fine. Any comments would be welcome here. I am a little stumped by these new features. I tried the above several times (incredu- lously, after having used cmos parts since the early 1980s with no problems). What IS going on, in your opinion? Comments, etc., are very welcome. Tia, -- Peter --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .