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simulating CD4007 (CD4009 ??) for linear application

[email protected] All Messages By This Member #160375 Hi! I am a LTSpice novice who is looking to simulate a CD4009 chip for a linear application. Specifically, in the electronotes newsletter #111, it is hinted that these can be used to make a simple VCA. My very naive approach has been to just copy down the arrangement of NMOS and PMOS shown on the CD4009 datasheet as shown, without tweaking any parameters or selecting "pick new transistor". The circuit I am trying to simulate seems to qualitatively do what it is supposed to after some tweaking, but with the RC values and and supply voltage as shown in the original schematic, it does not achieve nearly the performance claimed. I am wondering if there is any way to select NMOS and PMOS parameters to improve my simulation's accuracy to the actual CD4009. Any help is much appreciated! see files: Eli_R_CD4009_VCA_Question.asc? and photo album Eli_R_CD4009_VCA_Question datasheet: [Moderator's note:? The original Subject said "CD4007", but the body of the message refers only to "CD4009".? I have modified the Subject line to suggest the CD4009.]
Andy I All Messages By This Member #160379 Oops!? I "fat-fingered" when I typed what was supposed to be "CD4009" in the Subject line.? ?I have now fixed that. ? Sorry for messing up the messages in some of your email folders. ? Andy ? ?
Andy I All Messages By This Member #160381 On Sun, May 11, 2025 at 10:36 PM, <Eli.rosenkim@...> wrote: I am a LTSpice novice who is looking to simulate a CD4009 chip for a linear application. Specifically, in the electronotes newsletter #111, it is hinted that these can be used to make a simple VCA. ... Electronotes?- wow, I have not heard of them in a long time. ? My very naive approach has been to just copy down the arrangement of NMOS and PMOS shown on the CD4009 datasheet as shown, without tweaking any parameters or selecting "pick new transistor". The circuit I am trying to simulate seems to qualitatively do what it is supposed to after some tweaking, but with the RC values and and supply voltage as shown in the original schematic, it does not achieve nearly the performance claimed. I am wondering if there is any way to select NMOS and PMOS parameters to improve my simulation's accuracy to the actual CD4009. Any help is much appreciated! Somewhere, there might be a pair of .MODEL statements for the MOSFETs in those early CD4xxx parts.? The default NMOS and PMOS models are right for early 1970s, so the time period is about right for CD4xxx and maybe that works in your favor.? The other unknown is what are the W and L of each FET.? By default, you get W = L = 20 microns.? Fortunately the T.I. datasheet has lots of DC curves, which an enterprising student could use to compare with simulations and adjust W and L (and maybe the .MODEL parameters) to get a good fit.? Does that sound like a plan, and is the effort worth it? ? I notice the graph from the Electronotes #111 refers to a square wave audio input signal, which maybe suggests that the circuit might not be as clean as one would want for good audio. ? Andy ?

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