Fully differential reference driver for pipeline analog to digital converter

DETAILED DESCRIPTION The present invention applies a fully differential amplifier operating with negative feedback in the charge domain to source a stable reference voltage to, for example, a pipeline analog to digital converter (ADC).
In one aspect, a reference voltage value is established by applying a voltage dropped across a single resistor to differential inputs of the fully differential amplifier through a sample and hold circuit.
In a further aspect of the invention the sample and hold circuit is a crowbar network adapted to transfer electric potential across a pair of matched capacitors in response to the closing of a crowbar switch.
In a further aspect of the invention a fully differential amplifier is configured with capacitive feedback connections so as to exhibit unity gain.
In yet another aspect of the invention a control circuit is adapted to couple ancillary capacitors into the feedback circuit so as to controllably vary the gain exhibited by the differential amplifier.
In a still further aspect of the invention the differential output voltage output by the fully differential amplifier is divided with a further switched capacitor network to produce a divided reference voltage.
In other aspect of the invention, the reference voltage and divided reference voltage are applied at inputs to an ADC such as a pipeline ADC used in a CMOS active pixel sensor array (APS).
In an additional aspect of the invention, the voltage dropped across the single resistor is established by the action of a programmable current source.
The programmable current source is adapted to receive a control input corresponding to a required output current.
The control input may be a numerical (digital) value or may be an analog signal, one or the other being implemented according to the requirements of a particular system.
The control input may be a value received from an external controller, and may include a value based on a feedback signal taken from an output of the fully differential amplifier.
These and other advantages and features of the invention will be more clearly understood from the following detailed description of the invention which is provided in connection with the accompanying drawings