Pipelined analog-to-digital converter incorporating variable input gain and pixel read out analog front end having the same

摘要

A pipelined ADC incorporating variable input gain has a novel first stage generating a first digital output and a residue according to an analog input. The first stage comprises a novel MDAC. The MDAC comprises an operational amplifier, a feedback capacitor, a first sampling capacitor and a second sampling capacitor. First terminals of the feedback capacitor, the first sampling capacitor and the second sampling capacitor are connected to an inverted input terminal of the operational amplifier. A non-inverted input terminal of the operational amplifier is connected to a ground. In a sampling phase, second terminals of the feedback capacitor, the first sampling capacitor and the second sampling capacitor are connected to the analog input. In a charge transferring phase, second terminals of the feedback capacitor, the first sampling capacitor and the second sampling capacitor are respectively connected to the output terminal, a flash ADC output and the ground.

主权项

1. A pipelined analog-to-digital converter incorporating variable input gain, comprising:
N stages coupled in cascade, N being an integer larger than 1, a first stage of the N stages generating a first digital output and a residue of the first stage according to an analog input, a N-th stage of the N stages acquiring the residue from a previous stage ((N−1)th stage) to output an N-th digital output and a residue of the N-th stage; and an align and combine bits circuit, coupled to each of the N stages, acquiring the first digital output to N-th digital output to generate M-bits digital output, where M>N; wherein the first stage comprises: a flash analog-to-digital converter (flash ADC), generating a flash ADC output according to the analog input; and a multiplying digital-to-analog converter (MDAC), comprising an operational amplifier, a feedback capacitor, a first sampling capacitor and a second sampling capacitor, wherein a first terminal of the feedback capacitor, a first terminal of the first sampling capacitor and a first terminal of the second sampling capacitor are connected to an inverted input terminal of the operational amplifier, a non-inverted input terminal of the operational amplifier is connected to a ground; wherein the multiplying digital-to-analog converter (MDAC) operates in a sampling phase and a charge transferring phase; wherein in the sampling phase a second terminal of the feedback capacitor, a second terminal of the first sampling capacitor and a second terminal of the second sampling capacitor are connected to the analog input, an output terminal of the operational amplifier is connected to the inverted input terminal of the operational amplifier; wherein in the charge transferring phase the second terminal of the feedback capacitor is connected to the output terminal of the operational amplifier, the second terminal of the first sampling capacitor is connected to a corresponding reference voltage related to the flash ADC output, the second terminal of the second sampling capacitor is connected to the ground; wherein the residue of the first stage is an output of the multiplying digital-to-analog converter (MDAC) provided by the output terminal of the operational amplifier.