[sdiy] CMOS as voltage variable resistor

[Osamu (Sam) HOSHUYAMA]

Hello List,

Similar technique is used in Pearl Phaser PH-03 using 4069UBP.

http://www.mif.pg.gda.pl/homepages/tom/files/PH-03.gif

IC4 in the schematic is a 4069UBP.  4 inverters are used as 
variable transconductance amplifiers controlled by the 
voltage between Vdd and Vss.  A variable resister is formed by
each inverter (OTA) and corresoponding feedback resisters 
(680k and 220k).  Vss (pin 7) is driven by CV mixer (IC5, 
pins 5, 6, and 7) and Vdd (pin 14) is driven by another opamp 
(IC5, pins 1, 2, and 3), which is used with another inverter 
for CV cancellation based on assumption of matching of all 
the inverters.

It looks promising for all-CMOS VCF, if it works over that wide 
range like the VCO in EDN.

Osamu Hoshuyama,  Ottawa Canada

Theo wrote:
> 
> On the EDN website: http://www.ednmag.com
> there is an article "Inverters form three-phase VCO"
> that may be of interest.
> The current though the Vdd pin of the 74HCU04 is used
> to set the frequency of the oscillator.
> This might also work with a 4007 as variable resistor.
> 
> Theo