CD4046 VCO Math

[StephenGiles]

From memory only, I thought that the Deluxe Memory Man using 2 x MN3005, was driven by a 4047 clock with no buffer - need to check though.

Looked here -
http://sites.google.com/site/electroconducive/EHXDMM-Factory.jpg

It seems that I was partially correct, 3 x 4049 parallel inverter buffers were used on each clock line until 15/12/1978 - which is a long time ago

I'm sure that when I breadboarded it, the circuit I used had no buffer.

Anyway, your 4046 delay looks very interesting.

[TELEFUNKON]

Hey Nelson, just FYI - in my twiddlings with CD4046 and 3205's, I found them unable to drive more than one BBD.  You're going to either need to boost the clock outputs with transistors or use 3102s.  Unless you found something different... I was just experiencing unacceptable distortion.

+1. The clock inputs of BBDs are usually not buffered, for some reason I can't fathom (back to this later). The capacitance can be as high as three to four nanofarads, which is huge for a logic input. The clock/driver chips have both an oscillator and big-current drivers for the outputs. You can use 3102s, transistors, or put in a CD4049B (for buffered) chip and use three and three of the sections to drive the two clock phases. The 4049 is designed as a high current driver, a many kind of inverter. 

As for the fathoming, it has always made me wonder what they were thinking when they split out drivers from the delay array. That's not the kind of signal you want to run across a PCB if you're doing chip design. High speed clocks are hard enough without also making them be high power. It can't be that they didn't think of it - the guys at Reticon even showed them how, with the SAD512d and its integrated flipflop and drivers. It's bad practice to require high speed/high power clocks on ICs unless you just can't do anything else. Seems like they could have found the dozen or so gates to do this in an array with 8000 or more MOS devices already there. 

They maybe have thaught that two parallel traces carrying antiphased squarewaves behave like "twisted wires" towards their surrounding parts?

[StephenGiles]

Mike Irwin offered words of wisdom regarding the use of 3 and 3 inverter sections to drive the clock inputs of a BBD in a very old ADA Flanger thread.

[blueduck577]

Hey guys.  I've been wondering about this same subject for a while now.  I reread this thread and delved into the CD4046 appnote and got some useful information.

I present to you the CD4046 Parameter Calculation Spreadsheet!



Now, before you get too excited, while doing the math I took some shortcuts (mainly regarding the values of M1 and M2 if you read the appnote).  But for our purposes, the values I chose should be good enough to get you into the ballpark.

Since we are mostly talking about clocking BBDs here, I also added a column where you can put the number of stages in the BBD and it will calculate the delay.

To check my calculations, I took the component values from a Zombie Chorus and plugged them into the spreadsheet.  After the calculations were made, the spreadsheet indicated the delay time can be swept between 6 and 10ms.  Sounds about right for a chorus!  Just to be sure, I plugged these parameters into a chorus vst plugin I had.  Here are the results:

http://www.pitt.edu/~jjf33/zombie.mp3

First half is dry, then with the chorus applied.  Sure sounds like the zombie chorus to me!

So here is the link to the spreadsheet if you want it.  Simply change the constants in the top row, and everything else will be calculated and graphed.  Please don't kill me if its incorrect!
http://www.pitt.edu/~jjf33/cd4046.xlsx

I plan on heading up to my school's lab to experimentally verify these calculations sometime soon.

[toneman]

Forrest Mims said something about 4046s here:

http://books.google.com/books?id=STzitya5iwgC&pg=PA98&lpg=PA98&dq=%22forrest+mims%22+4046&source=bl&ots=Le1kHCeJsM&sig=-JLq2bE4l2-QRMzVUGonGWTLtqA&hl=en&ei=ZcsXTvy8E-PeiALqp9HRBQ&sa=X&oi=book_result&ct=result&resnum=1&ved=0CBUQ6AEwAA#v=onepage&q&f=false

This is frome the Forrest Mims Scrapbook of Circuits.

Maybe U can find a pdf of it(?)

[ExpAnonColin]

BlueDuck, this will be helpful.  Are you a Pitt affiliate?  I live in Pittsburgh.

-Colin

[blueduck577]

Yeah, I'm a pitt student.

[PVP]

Someone who is still looking for formulas for CD4046. See page 28.