High-linearity variable gain amplifier

Abstract

The invention discloses a high-linearity variable gain amplifier which mainly solves the problem that existing similar amplifiers are poor in linearity. The amplifier comprises a first amplifying circuit (1), a current multiplexing module (3), a second amplifying circuit (2) and a cascode amplifying circuit (5) which are connected in sequence, an intermediate node of the cascode amplifying circuit (5) is connected with a current control module (6), and the current control module (6) is used for controlling the gain of the whole amplifier by controlling the current flowing through the cascode amplifying circuit (5). The other input end of the first amplifying circuit (1) is connected with a linearity improving module (4) which is used for simultaneously offsetting a second-order nonlinear term and a third-order nonlinear term of the main amplifying circuit and improving the linearity of the amplifier. On the premise of ensuring high gain and low additional phase shift of the circuit, the linearity of the variable gain amplifier can be effectively improved, and the circuit is simple in design, low in cost and capable of being used in a wireless communication radio frequency front-end chip.

Description

technical field [0001] The invention belongs to the technical field of radio frequency integrated circuits, and particularly relates to a variable gain amplifier, which can be used in a radio frequency front-end chip of wireless communication. Background technique [0002] The variable gain amplifier VGA is the key module of the radio frequency transceiver. Its function is to adjust the amplitude and power of the received and transmitted signals, to compensate the gain between different channels of the phased array and to reduce the side lobes in the phased array transceiver system. level; as a gain control unit, the variable gain amplifier needs to have enough gain dynamic range to compensate for the gain variation of any scanning branch, and should not introduce additional phase shift when adjusting the gain, otherwise it will deteriorate the phased array The scanning accuracy of the system; the variable gain amplifier is at the back end of the RF receiver chain, and its l...

AI Technical Summary

Problems solved by technology

Although the above patents can improve the linearity through the inherent structure of the closed-loop variable gain amplifier, they cannot optimize the linearity to the best

[0004] Mohammad Reza Nikbakhsh disclosed a ring-opening can variable gain amplifiers, such as figure 1 As shown, the linearity improvement module of the variable gain amplifier is composed of an NMOS transistor working in the subthreshold region. The NMOS transistor is connected in parallel at both ends of the main amplifier transistor, and the third-order nonlinear term is used to reverse the phase under different biases. It can effectively offset the third-order nonlinearity of the transconductance to improve the linearity, but the second-order intermodulation nonlinearity of the NMOS transistor has the same phase in the two bias states, and its accumulation will limit the linearity of the circuit. This effect is more serious when the circuit works in the millimeter wave frequency band, and even makes the linearity improvement effect caused by the third-order nonlinearity disappear.

[0005] In his paper "Research and Design of Ultra-Wideband Variable Gain Amplifier Based on BiCMOS Process" (Xidian University, Master's Thesis of Electronic Science and Technology, November 2015), Zhou Wen disclosed an open-loop variable gain amplifier. Variable gain amplifier, the variable gain amplifier uses a common base as the differential current steering structure of the input circuit, and introduces emitter negative feedback resistors and capacitors to improve linearity and widen bandwidth, but the introduction of negative feedback resistors and capacitors will greatly reduce the gain

In addition, the additional phase shift penalty of this variable gain amplifier is severe

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