Sampling switch having an independent “on” impedance

A sampling device for sampling an input signal, the sampling device comprising:

• a sampling switch for creating samples of the input signal, the sampling switch having a turn on voltage and an impedance;
• and
• a control device for generating a control signal for controlling the sampling switch, the control device comprising:
• a reference voltage source for generating a reference voltage;
• and
• a control switch for generating a control switch voltage, the control switch voltage comprising the sum of the input signal and the turn on voltage, and the control signal comprising the sum of the control switch voltage and the reference voltage.

A method of making an on impedance of a sampling switch independent of an input signal, the sampling switch comprising a gate to source voltage, a threshold voltage, and an on impedance corresponding with the difference between the gate to source voltage and the threshold voltage, the method comprising:

• providing a reference voltage in response to the sample signal;
• generating a control signal in response to the sample signal to control the sampling switch, wherein the step of generating a control signal comprises:
• summing the input signal and the threshold voltage to generate a control circuit voltage in response to the sample signal;
• summing the control circuit voltage and the reference voltage to generate the control signal;
• and
• differentiating the control signal from the input signal to generate the gate to source voltage.

An analog to digital converter for converting an analog input signal into a digital output signal, the analog to digital converter comprising:

• a sampling device for sampling the analog input signal and creating output samples, the sampling device comprising:
• a sampling transistor for creating samples of the input signal in response to the sample signal, the sampling transistor having a gate to source voltage, a threshold voltage, and, an on impedance corresponding with the difference between the gate to source voltage and the threshold voltage;
• and
• a control device for controlling the sampling transistor by generating a control signal in response to the sample signal, the control device comprising:
• a bootstrap reference voltage source for providing a reference voltage in response to the sample signal;
• and
• a control circuit for generating a control circuit voltage in response to the sample signal, the control circuit voltage comprising the sum of the input signal and the threshold voltage, the control signal comprising the sum of control circuit voltage and the reference voltage, and the gate to source voltage comprising the difference between the control signal and the input signal;
• and
• a holding device for holding the output samples;
• a quantizing device for quantizing the output samples;
• and
• an encoding device for encoding the quantized output samples.