Electronotes/AN-23 - The CA3080 as a voltage-controlled resistor: Difference between revisions

[[File:AN23 fig 1a.jpg|thumb|right|250px|Fig. 1a.jpg]][[File:AN23 fig 1b.jpg|thumb|right|250px|Fig. 1b.jpg]][[File:AN23 fig 1c.jpg|thumb|right|250px|Fig. 1c.jpg]][[File:AN23 fig 1d.jpg|thumb|right|250px|Fig. 1d.jpg]][[File:AN23 fig 1e.jpg|thumb|right|250px|Fig. 1e.jpg]][[File:AN23 fig 2a.jpg|thumb|right|250px|Fig. 2a.jpg]][[File:AN23 fig 2b.jpg|thumb|right|250px|Fig. 2b.jpg]]In AN-22, we looked at the CA3080 Operational Transconductance Amplifier (OTA) as a voltage-controlled gain source. Here, we will use these previous ideas as a jumping-off point to see how the CA3080 can be made to act like a voltage-controlled resistor (VCR). In these applications, the CA3080 is used in its linear mode, so signals at the actual input pins are limited to (generally attenuated to) ±10 mV. In the cases below we will not be showing the actual circuitry that controls the control current (Ic<math>I_{c}</math>) of ththe CA3080, but the reader can consider this circuitry to be similar to that shown in AN-22. The fact that the CA3080 could look like a resistor is implied by the name "transconduct ance" and can be seen by writing the basic equation for the CA3080 as: