Track and hold amplifiers

An optical receiver, comprising:

• an analog-to-digital converter (ADC);
• and
• a track and hold amplifier (THA) coupled to the ADC and including:
• an emitter follower transistor coupled to each of an input of the THA and an output of the THA;
• a charging node coupled between the output and a voltage supply, the charging node further coupled between a collector and an emitter of the emitter follower transistor;
• and
• a cascode switch including a first path coupled to the input and a second path coupled to the output, wherein each of the first and second paths includes a bipolar transistor and a field-effect transistor (FET), and wherein the first path and the second path are substantially symmetrical and respectively electrically passively couple the input and the output to a common node, the cascode switch configured to:
• cause the emitter follower transistor to operate in a conductive state and charge the charging node during a track mode;
• and
• cause the emitter follower transistor to operate in a non-conductive state to isolate the charging node from the input during a hold mode.

A device, comprising:

• a plurality of emitter follower transistors, each emitter follower transistor of the plurality of emitter follower transistors coupled to each of an input and an output;
• a plurality of charging nodes coupled to the output, each charging node of the plurality of charging nodes further coupled between a collector and an emitter of at least one emitter follower transistor of the plurality of emitter follower transistors;
• and
• a plurality of cascode switches, each cascode switch of the plurality of cascode switches including a first path coupled to the input and a second path coupled to the output, wherein each of the first and second paths includes a bipolar transistor and a field-effect transistor (FET), and wherein the first path and the second path are substantially symmetrical and respectively electrically passively couple the input and the output to a common node, each cascode switch configured to:
• cause an emitter follower transistor of the plurality of emitter follower transistors to operate in a conductive state and charge a charging node of the plurality of charging nodes during a track mode;
• and
• cause the emitter follower transistor to operate in a non-conductive state to isolate the charging node from the input during a hold mode.

A method, comprising:

• receiving an input signal at an input coupled to an emitter follower transistor including a charging node coupled between a collector and an emitter of the emitter follower transistor;
• configuring a cascode switch to have a first path coupled to the input and a second path coupled to an output, wherein each of the first and second paths includes a bipolar transistor and a field-effect transistor (FET), and wherein the first path and the second path are substantially symmetrical, and electrically passively coupling the input and the output to a common node to cause the emitter follower transistor to operate in a conductive state to couple the input to each of a charging node and the output during a track mode;
• and
• configuring the cascode switch to cause the emitter follower transistor to operate in a non-conductive state to isolate the input from each of the charging node and the output during a hold mode.