[sdiy] OTA as Voltage Controlled Resistor

[Justin Owen]

Hello,

The LM13700 data sheet shows a schem (Fig. 10) for a 'Floating Voltage Controlled Resistor' - this seems to be a double-ended circuit as opposed to the FET-based circuits (and the the LM13700 circuit in Fig. 9) which (from memory) are single-ended.

My questions...

1) Can the double-ended circuit be used to replace a standard discrete resistor - i.e. is either 'end' replacing a leg/pin of a resistor?

2) Assuming the answer to #1 is 'yes' - has anyone got any idea of what sort of resistance range could be pulled from an OTA?  

3) Can someone provide examples of how a single-ended circuit might be used?

In short, I'm wondering if an OTA VCR might be a suitable replacement for a vactrol under certain circumstances.

Thanks,

Justin