Inverse function method for semiconductor mixer linearity enhancement

Abstract

The mixer circuit includes a differential rf input driver; a differential local oscillator input circuit coupled to the differential rf input driver; a non-linear load coupled to the differential local oscillator input circuit wherein the non-linear load compensates for non-linearity of the differential rf input driver. The non-linear load has a V-I (voltage-current) transfer function the inverse of the input driver. This improves the mixer linearity without sacrificing the Gain or Noise Figure.

Description

FIELD OF THE INVENTION [0001] The present invention relates to electronic circuitry and, in particular, to semiconductor mixer circuits. BACKGROUND OF THE INVENTION [0002] A semiconductor mixer's linearity is crucial to the overall linearity of RF transceiver links, and thus crucial to its ability to reject the interferers. A traditional prior art Gilbert-cell active mixer uses linear semiconductor resistor load in conjunction with the non-linear V-I (voltage-current) input drivers. The linearity is limited by how good you can linearize the input drivers and how much other performance loss (Gain, Noise Figure, etc.) you are willing to trade. [0003] Mixers play an important role in the wireless transceiver chain. It follows the Low Noise Amplifier (LNA) or possibly image rejection filter, translates the RF signal to the IF or baseband signal, and sends the (amplified) signal to the next stage. The linearity of the mixer is a critical parameter as unwanted interferers, if not signific...

AI Technical Summary

Benefits of technology

[0006] The mixer circuit includes a differential rf input driver; a differential local oscillator input circuit coupled to the differential rf input driver; a non-linear load coupled to the differential local oscillator input circuit wherein the non-linear load compensates for non-linearity of the differential rf input driver. The non-linear load has a V-I (voltage-current) transfer function the inverse of the input driver. This improves the mixer linearity without sacrificing the Gain or Noise Figure.

Problems solved by technology

The linearity is limited by how good you can linearize the input drivers and how much other performance loss (Gain, Noise Figure, etc.) you are willing to trade.

Even though it has been shown that the differential output voltage is still a linear function of the differential input voltage if the input common mode voltage is a constant and the quadratic I-V (current-voltage) relationship is valid, the RF input common mode voltage cannot be guaranteed to be a constant due to the LO kickback and parasitic coupling.

Furthermore, the deep sub-micron CMOS technology cannot guarantee the quadratic I-V relationship.

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