An Operational Amplifier for Pipelined Analog-to-Digital Converters

Abstract

The invention discloses an operational amplifier for a pipelined analog-to-digital converter, comprising: a first main operational amplifier and a second main operational amplifier; the first main operational amplifier includes first cascode P-type amplifiers connected in sequence The transistor pair, the second cascode P-type transistor pair, the first cascode N-type transistor pair, the first common-source N-type transistor pair, the source of the first common-source N-type transistor pair is connected to the first Tail current N-type transistor; the second main operational amplifier includes a third cascode P-type transistor pair and a second common-source N-type transistor pair connected in sequence, and the source of the second common-source N-type transistor pair A second tail current N-type transistor is connected; wherein, the drains of the first cascode P-type transistor pair are respectively connected to the drains of the third cascode P-type transistor pair through compensation capacitors. Compared with the prior art, the invention can greatly improve the gain and precision of the operational amplifier under low voltage conditions.

Description

technical field [0001] The invention belongs to the field of operational amplifiers, in particular to an operational amplifier used for pipeline analog-to-digital converters. Background technique [0002] With the development of CMOS technology, the characteristic size of MOS transistors is continuously reduced, and the characteristic frequency is continuously increased, which also leads to the continuous decline of the intrinsic gain of MOS transistors. At the same time, the power supply voltage continues to decrease, which also makes the design of high-gain operational amplifiers particularly difficult. . The operational amplifier in the first-stage MDAC in the pipeline analog-to-digital converter is extremely harsh, making the design of high-precision and high-speed pipeline ADC particularly difficult. [0003] Traditional pipeline operational amplifiers and residual operational amplifiers of various stages are usually realized by closed-loop high-performance amplifiers....

AI Technical Summary

Problems solved by technology

This structure increases the output impedance and increases the open-loop gain by adding an auxiliary op amp. However, the added auxiliary op amp will introduce new parasitic capacitance, thereby increasing the pole and reducing the bandwidth of the entire op amp.

The bandwidth of the comparator, the noise on the sampling capacitor, and the load capacitance of each stage all affect the accuracy of the pipeline

Additionally, conventional pipelined op amps cannot achieve high gain at low supply voltages

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