A differential pair input circuit with constant transconductance

Abstract

The invention discloses a novel transconductance constant differential pair input circuit comprising an NMOS differential input pair and a PMOS differential input pair. Tail current values of the NMOS differential input pair and the PMOS differential input pair are both I; the differential pair input circuit controls on-off current source of a 3-times tail current source switch tube via monitoring voltage of an intermediate node (A) of the PMOS differential input pair and an intermediate node (B) of the NMOS differential input pair and voltage value fluctuation; and the current source is connected to one part of the differential input pair and working as the tail current. With monitoring voltages of the nodes (A,B), the 3-times tail current source switch tube bias voltage fluctuates to a proper value to control on-off of the switch tube to control changes of the differential pair tail currents; and transconductance input and constant can be achieved.

Description

technical field [0001] The invention relates to the field of CMOS analog circuit design, in particular to a differential pair input circuit with constant transconductance. Background technique [0002] In the rail-to-rail operational amplifier (Rail-to-RailOPAMP) design, the input stage is required to have a constant transconductance function (constant transconductance) from the low potential of the power supply to the high potential, that is, within the rail-to-rail voltage range ). A single PMOS or NMOS differential input pair will be in the cut-off, sub-threshold, linear and saturated four operating regions in the full voltage range, and its transconductance changes from zero to the maximum value. [0003] Since the PMOS transistor is turned on at a low gate voltage, it is turned off at a high gate voltage; while the NMOS transistor is just the opposite, it is turned off at a low gate voltage and turned on at a high gate voltage. According to this characteristic, when t...

AI Technical Summary

Problems solved by technology

This pair of contradictions is not easy to reconcile. In some circuit analysis, it often occurs that the drain-source voltage of the switch tube is too large when it is turned on, causing the tail current source tube to be in the linear region.

On the other hand, the 3 times current mirror constant transconductance circuit requires accurate bias voltage VBIASN, VBIASP, such as figure 2 As shown, this increases the design complexity of the circuit; at the same time, under some extreme circuit technology, environment, and power supply conditions, the generated bias voltage is likely to no longer meet the circuit requirements

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