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A practical realization of the switch circuit requires a voltage-current converter (V🠖I), and a source of bias currents, shown below.

The various currents are derived from a 100uA reference. An LM334 could generate this current, for example. Another option would be REF200, but it costs an order of magnitude more.

The V🠖I converter maintains 3V at the emitter of Q23, and uses R8 to load input voltage using 3V as the reference. The current passes through Q23.

The current then gets subtracted from the 300uA reference, and enters the Q1-Q2 current steering pair. When the switch is turned on, Q2 conducts and passes the current through the output load resistor R5.

The V-I converter could be done with an op-amp Howland current pump, but that would take good resistors and a good op-amp to be better than the discrete circuit. At 30kHz, you'd need an op-amp with GBW to 10MHz to maintain reasonable distortion, if you care about that.

An op-amp could provide the gain and buffering of the switch output, of course.

A practical realization of the switch circuit requires a voltage-current converter (V->I), and a source of bias currents, shown below.

The various currents are derived from a 100uA reference. The current mirror used is an improved 4-transistor Wilson mirror. The additional transistor buffers the base currents and allows paralleling of multiple current output stages in one mirror.

An LM334 could generate the reference cut rent. Another option would be REF200, but it costs an order of magnitude more.

The V->I converter uses a unipolar output op-amp to maintain 3V at the emitter of Q23. R8 loads the input voltage using 3V as the reference, converting it into current. The current passes through Q23.

Perhaps there could be a cascode transistor behind Q23 to increase the accuracy without slowing down the response, but at 5V there’s not much voltage drop to work with – it’d need to be an inverted cascode.

Q23 and the cascode, if any, would benefit from base current compensation, to improve gain accuracy. Q23 could also be a high transconductance low voltage mosfet.

The current then gets subtracted from the 300uA reference, and enters the Q1-Q2 current steering pair. When the switch is turned on, Q2 conducts and passes the current through the output load resistor R5. The current steering could also be done by mosfets, bringing the gain back to 1.000 if combined with a mosfet Q23.

The V->I converter could be done with an op-amp Howland current pump, but that would take good resistors and a good op-amp to be better than the discrete circuit. At 30kHz, you'd need an op-amp with GBW to 10MHz to maintain reasonable distortion, if you care about that.

An op-amp could provide the gain and buffering of the switch output, of course.

Getting a transistor acting as a good switch takes a bit of work by the surrounding circuitry :)

^{simulate this circuit – Schematic created using CircuitLab}

^{simulate this circuit}

^{simulate this circuit – Schematic created using CircuitLab}

^{simulate this circuit}

The V-I converter could be done with an op-amp Howland current pump, but that would take good resistors and a good op-amp to be better than the discrete circuit. At 30kHz, you'd need an op-amp with GBW to 10MHz to maintain reasonable distortion, if you care about that.

An op-amp could provide the gain and buffering of the switch output, of course.