behavioural opamp 02 PUBLIC

Using the TANH() function, a near ideal behavioural opamp or comparator with a rail to rail limited output voltage swing can be made.

This model is almost the same as behavioural opamp 01 except that it uses a current source with a resistor, Rout, in parallel to create a Norton equivalent source.

Using the TANH() function, a near ideal behavioural opamp or comparator with a rail to rail limited output voltage swing can be made.

This model is almost the same as behavioural opamp 01 except that it uses a current source with a resistor, Rout, in parallel to create a Norton equivalent source. In some circumstances, this may simulate better. The parallel capacitance limits the open loop bandwidth but is there as a convergence aid rather than a bandwidth defining component because the pole formed by it and Rout will be affected by the external load resistances.

Using a Norton source, a simple transconductance amplifier (Iout/Vin) can be modelled.

This model has infinite input common mode and differential range, input impedance and bandwidth, zero propagation delay and output impedance, and draws no input or supply current.

in is the input signal.

inp is the non-inverting input

fb is the inverting input

vcc is the positive supply rail

vee is the negative supply rail

Avol is the open loop gain. Note that Avol is divided by the rail to rail difference to make the actual open loop gain supply voltage independent.

Making Rfb open circuit allows the circuit to function as a comparator.