Linear transconductance circuits having class AB amplifiers parallel coupled with concave compensation circuits

A transconductance circuit characterized by a voltage to current transfer function, the transconductance circuit comprising:

• an input terminal;
• an output terminal;
• a class AB transconductance amplifier coupled across the input and output terminal;
• a first concave compensation circuit parallel coupled with the class AB transconductance amplifier, the first concave compensation circuit having a positive offset;
• and
• a second concave compensation circuit parallel coupled with the class AB transconductance amplifier, the second concave compensation circuit having a negative offset.

An operational amplifier comprising:

• an input stage characterized by a voltage to current transfer function, the input stage comprising:
• a class AB transconductance amplifier, wherein the class AB amplifier includes a pair of differentially coupled diamond followers, each diamond follower having four transistors and two bias current sources, the transconductance of the first class AB amplifier being a function of transistor gain and the available bias current;
• and
• a concave compensation circuit including two differential transistor pairs, the class AB amplifier and concave compensation circuit coupled in parallel across differential input and output pairs, wherein the concave transconductance gain of the concave compensation circuit improves linearity of the voltage to current transfer function of the input stage by compensating for the convex transconductance gain of the class AB amplifier;
• and a second stage coupled in series with the input stage.

A multiple stage circuit comprising:

• a transconductance stage suitable for converting a voltage signal into a current signal, the transconductance stage having a convex transconductance amplifier, a first concave transconductance amplifier having a positive offset, the convex amplifier and first concave amplifier coupled in parallel, inputs of the two parallel coupled transconductance amplifiers being directly coupled while the outputs of the two parallel coupled transconductance amplifiers are not directly coupled, and a second concave transconductance amplifier having a negative offset, the negative and positive offsets being selected to improve linearity of the multiple stage circuit;
• and
• a plurality of stages subsequent to the transconductance stage, the plurality of stages subsequent to the transconductance stage including:
• a second stage responsive to a current signal, wherein an input of the second stage is coupled to an output of the convex transconductance amplifiers;
• and
• a third stage responsive to a current signal, wherein an input of the third stage is coupled to an output of the concave transconductance amplifiers.

A multiple stage circuit comprising:

• a transconductance stage suitable for converting a voltage signal into a current signal, the transconductance stage having a convex transconductance amplifier and a concave transconductance amplifier coupled in parallel, inputs of the two parallel coupled transconductance amplifiers being directly coupled while the outputs of the two parallel coupled transconductance amplifiers are not directly coupled, wherein the concave transconductance amplifier is a tanh doublet;
• and
• a plurality of stages subsequent to the transconductance stage, the plurality of stages subsequent to the transconductance stage including:
• a second stage responsive to a current signal, wherein an input of the second stage is coupled to an output of the convex transconductance amplifiers;
• and
• a third stage responsive to a current signal, wherein an input of the third stage is coupled to an output of the concave transconductance amplifiers.