An operational amplifier, a level conversion circuit and a programmable gain amplifier

Abstract

The embodiment of the invention discloses a level switching circuit which comprises two operational amplifiers and a common-mode feedback loop. A substrate and a PMOS source follower which is connected with a source electrode are inserted in a P point of each operational amplifier, so that big difference oscillation amplitude 3.3V high common-mode level is horizontally moved to 1.2V low common mode level with low degree of distortion, and the difference oscillation amplitude is kept unchanged. The common-mode feedback loop receives output signals of the two operational amplifiers, common-mode taking operation is conducted on the two output signals, an obtained common-mode value is compared to a set reference voltage, and the comparison result is used as a feedback signal to be output to the two operational amplifiers. The embodiment of the invention further provides the operational amplifiers and a programmable gain amplifier. According to the level switching circuit, the operational amplifiers and the programmable gain amplifier, the function of switching from low level to high level and the function of switching from the high level to the low level can be achieved at the same time, and the demand for large outputting oscillation amplitude and high linearity is met.

Description

technical field [0001] The invention relates to the technical field of semiconductors, in particular to an operational amplifier, a level conversion circuit and a programmable gain amplifier. Background technique [0002] In the analog-digital hybrid chip, it is often necessary to level-shift the continuous analog signal at the analog front end, while ensuring the quality of the shifted signal (such as swing amplitude, linearity, etc.). Usually, considering performance, voltage margin and other reasons, the analog front-end circuit is often designed with IO devices working in the high-voltage domain. In consideration of reasons such as power consumption and area, digital and analog-to-digital converters are implemented using core devices operating in the low-voltage domain. Therefore, the level conversion circuit needs to move the analog signal from the high-voltage domain to the low-voltage domain, which not only involves the conversion of the voltage domain, but also invo...

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Problems solved by technology

[0009] (1) The conversion function from high level to low level cannot be realized;

[0010] (2) Due to the channel length modulation effect of MOS transistors, with the different voltages at both ends of the drain and source, the same drain current will also lead to different gate-source voltages Vgs

However, when the frequency of the input signal Vin increases, the parasitic capacitance increases due to the increase of the channel length. On the one hand, the maximum input signal frequency is limited, and on the other hand, the increased parasitic capacitance will also deteriorate the linearity of the output signal Vout.

[0011] (3) When the open-loop source follower drives a large capacitive or resistive load, as the input signal changes, the load will draw different currents from the current source Is10, which will change the current flowing through the PMOS transistor M10 Current, so that the gate-source voltage Vgs changes with the input signal, which deteriorates the linearity of the output signal Vout

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