COMMON MODE INPUT CONTROL FOR SWITCHED CAPACITOR AMPLIFIER IN PIPELINE ANALOG-TO-DIGITAL CONVERTER
A common mode bias circuit may include a weak common mode bias generator and a common mode bias capacitance. During a first state of the common mode bias circuit, the weak common mode bias generator may be coupled to the common mode bias capacitance and may impart to them a predefined common mode signal level. During a second state of the common mode bias circuit, the common mode bias capacitance may be coupled to differential inputs of an amplifier in a manner that establishes an input common mode level for the amplifier.
1 . A common mode bias circuit comprising:
a common mode bias generator; and
a common mode bias capacitance,
wherein the common mode bias circuit is configured such that:
during a first state of the common mode bias circuit, the common mode bias generator is coupled to the common mode capacitance and imparts to it a predefined common mode signal level, and
during a second state of the common mode bias circuit, the common mode bias capacitance is coupled to differential inputs of an amplifier in a manner that establishes an input common mode level for the amplifier.
2 . The common mode bias circuit of claim 1 wherein the common mode bias generator is weak.
3 . The common mode bias circuit of claim 1 wherein the common mode bias circuit is part of a pipeline analog-to-digital converter.
4 . A method of setting an input common mode level of a differential amplifier comprising:
using a common mode bias generator and a common mode bias capacitance to establish a predefined signal level during a first state; and
using the common mode bias capacitance during a second state to transfer a predefined signal level to differential inputs of the amplifier.
5 . The method of claim 4 wherein the common mode bias generator is weak.
6 . The method of claim 4 wherein the common mode bias circuit is part of a pipeline analog-to-digital converter.