Differential high speed track and hold amplifier

A differential track and hold amplifier, comprising:

• a first transconductance amplifier responsive to an input signal and having first and second outputs;
• a second transconductance amplifier responsive to a control signal for rendering said second transconductance amplifier operative and having first and second inputs and first and second outputs, said first and second inputs of said second transconductance amplifier respectively coupled to said first and second outputs of said first transconductance amplifier;
• a resistance circuit coupled between said first and second outputs of said second transconductance amplifier and said first and second outputs of said first transconductance amplifier;
• a subtractor circuit coupled between a first supply voltage terminal and said first and second outputs of said transconductance amplifier;
• a capacitor;
• a switching circuit responsive to said control signal and having first and second inputs respectively coupled to said first and second outputs of said first transconductance amplifier, said switching circuit for transferring signals appearing at said first and second outputs of said first transconductance stage for use in storing a voltage across said capacitor;
• an output stage responsive to said voltage appearing across said capacitor for providing an output signal;
• and
• wherein a common mode voltage of signals appearing at first and second inputs of said switching circuit is reduced when said second transconductance amplifier is rendered operative.

A method for tracking and holding an input signal of a track and hold circuit, the method comprising the steps of:

• receiving the input signal;
• converting the input signal into a first differential current signal;
• operating in a tracking mode by;
• closing a switching circuit;
• disabling a substraction function of a substractor circuit;
• converting the first differential current signal into a differential voltage signal using the substractor circuit, the differential voltage signal appearing at an input of the switching circuit;
• and
• charging a capacitor with said differential voltage signal;
• operating in a holding made by;
• opening the switching circuit to store said voltage appearing across said capacitor, wherein the voltage appearing across said capacitor is transmitted to an output of the track and hold circuit;
• converting said differential voltage signal into a second differential current signal using an amplifier;
• and
• enabling the substraction function of the substractor circuit to substract the second differential current signal from the first differential current signal and provide the difference to the input of the switching circuit.

A method for tracking and holding an input signal of a track and hold circuit, the method comprising the steps of:

• receiving the input signal;
• converting the input signal into a first differential current signal;
• operating in a tracking mode by;
• closing a switching circuit;
• disabling a substraction function of a substractor circuit coupled to said switching circuit;
• converting the first diferential current signal into a differential voltage signal using the substractor circuit, the differential voltage signal appearing at an input of a switching circuit;
• and
• charging a capacitor with said differential voltage;
• operating in a holding mode by;
• opening the switching circuit to store said differential voltage signal across said capacitor by turning off a set of current sources and turning off a set of transistors, wherein a first transistor of said set of transistors is coupled to a first terminal of said capacitor and a second transistor of said set of transistors is coupled to a second terminal of the capacitor, wherein the voltage appearing across said capacitor is transmitted to an output of the track and hold circuit;
• converting said differential voltage signal into a second differential current signal using a transconductance amplifier;
• and
• enabling the substractor function of the substractor circuit to substract the second differential current signal from the first differential current signal and provide the difference to the input of the switching circuit.