Fully-differential amplifier and residual gain circuit using fully-differential amplifier

Abstract

The invention relates to a fully-differential amplifier. The fully-differential amplifier comprises first and second complementary differential input pairs, and further comprises a positive feedback system; the positive feedback system is connected with the first and second complementary differential input pairs, and used for providing positive feedback to the first complementary differential input pair and the second complementary differential input pair; the positive feedback system comprises a third complementary differential input pair; the third complementary differential input pair comprises a first PMOS transistor and a second PMOS transistor; the grids of the first PMOS transistor and the second PMOS transistor are separately connected with the output ends of the first complementary differential input pair and the second complementary differential input pair; and the drains of the first PMOS transistor and the second PMOS transistor are separately connected with the output ends of the second complementary differential input pair and the first complementary differential input pair. On the basis of the fully-differential amplifier, the invention further provides a residual gain circuit adopting a related level shift method. The fully-differential amplifier disclosed by the invention has the advantages of being low in power consumption, rapid in speed, high in conversion rate and simple in circuit structure; and, with the help of the related level shift technology, the high-speed and high-precision residual gain circuit can be realized.

Description

technical field [0001] The invention belongs to the field of analog-to-digital converters, and more specifically relates to a fully differential amplifier and a residual gain circuit using the same. Background technique [0002] Pipeline analog-to-digital converter (ADC) is a kind of high-speed and high-precision analog-to-digital converter, which is widely used in communication systems and complementary metal oxide semiconductor (CMOS) image sensors. In the traditional pipeline ADC design, the transconductance operational amplifier (OTA) accounts for the main part of the power consumption in the analog domain. Therefore, designing a high-performance OTA is crucial to the entire ADC. [0003] Existing OTAs are generally divided into telescopic OTAs, foldable OTAs, and two-stage OTAs. As shown in Figure 1(a), it is a telescopic cascode OTA, which has a large gain, the fastest speed, and the lowest power consumption, but its input and output swings are the smallest. When conn...

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Problems solved by technology

As shown in Figure 1(a), it is a telescopic cascode OTA, which has a large gain, the fastest speed, and the lowest power consumption, but its input and output swings are the smallest. When connected to unity gain, it works The range is very small; Figure 1(b) is a folded cascode OTA, which has a large input and output swing, but its power consumption is double that of the telescopic cascode OTA, and the noise The performance and gain are also worse than the sleeve-type cascode OTA; Figure 1(c) is a two-stage (Two-Stage) OTA, its gain and output swing are large, but its frequency response is the worst, usually need to block capacitor (RC) compensation network, and the power consumption is the largest among the three types of OTA

With the continuous development of CMOS technology, especially when the power supply voltage is reduced below 1V, the intrinsic gain of the transistor drops rapidly, and the input and output swings of the sleeve OTA and the folding OTA are severely limited, and their gain is also greatly reduced. Its performance can no longer meet the requirements of low-voltage design; two-level OTA can meet the above requirements, but its power consumption is the largest, which does not meet the design concept of low power consumption

Usually, the way to solve the gain problem is to introduce gain-boosting technology on the cascode tube in the telescopic OTA and folded OTA to improve the open-loop gain of the OTA, but this technology will introduce complex frequency response, the increased power consumption is also larger

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