Voltage-Controlled Low-Pass Filter with LM13600 OTA
Below is a circuit that demonstrates one use of an OTA using an LM13600. Take a note that the strange symbol stand for OTA. In this circuit, negative feedback is employed which is low-pass filter whose corner frequency can be electrically adjusted. We can a filter that would tune from 2700 Hz to 9000 Hz approximately for the values shown.
The gain is rolls off at 20 dB/decade and unity below the corner frequency, a first-order response like an RC circuit. The electrical controllability of the corner frequency is the feature which is here simulated by rotating a potentiometer. You will not exceed the maximum 2 mA for the bias current is guaranteed by the 12k fixed resistor. In this circuit, the voltage at pin 1 is -10.8V (two diode drops above the negative supply). The pin numbers for one of the amplifiers are shown, going down the left-hand side of the chip. For other amplifiers, the pins are in the same order on the other side. We have to take a note the unusual location of the supply pins.