Analog-to-digital conversion

摘要

An analog-to-digital conversion apparatus 10 comprises a plurality of analog-to-digital converters 30 and a ramp generator 20. Each of the analog-to-digital converters 30 comprises an analog signal input for receiving an analog signal level and a ramp signal input. A control stage is arranged to compare the ramp signal with the analog signal level and, based on the comparison, to enable a counter provided at the analog-to-digital converter or to latch a digital value received from a counter. The control stage comprises a comparator in the form of a first differential amplifier with a first branch connected to the input for receiving the ramp signal, a second branch connected to the analog signal input and an output, and a biasing current source for biasing the first differential amplifier. A feedback circuit controls the biasing current source. The feedback circuit comprises a second differential amplifier OP1 with a first input connected to a node 46 on the first branch and a second input connected to a reference voltage VB such that the node on the first branch is maintained at a substantially constant voltage.

主权项

1. An analog-to-digital conversion apparatus comprising:
a plurality of analog-to-digital converters; a ramp generator which is arranged to generate a ramp signal for distribution to the plurality of analog-to-digital converters; wherein each of the analog-to-digital converters comprises:
an analog signal input for receiving an analog signal level;a ramp signal input for receiving the ramp signal;a control stage which is arranged to compare the ramp signal with the analog signal level received at the analog signal input and, based on the comparison, to enable a counter provided at the analog-to-digital converter or to latch a digital value received from a counter, the control stage comprising:
a comparator in the form of a first differential amplifier with a first branch connected to the input for receiving the ramp signal, a second branch connected to the analog signal input and an output;a variable biasing current source for biasing the first differential amplifier;a feedback circuit for controlling the variable biasing current source, wherein the feedback circuit comprises a second differential amplifier with a first input connected to a node on the first branch and a second input connected to a reference voltage such that the node on the first branch is maintained at a substantially constant voltage during all comparison states of the comparator.