Active Mixer GM3 Cancellation for LO-Amplitude Linearity
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Solution Overview
Problem
Active mixer circuits operating at high frequencies, such as millimeter wave frequencies, face challenges in maintaining linearity due to variations in third-order transconductance (gm3) caused by the range of local oscillator signal amplitudes, leading to third-order intermodulation distortion and reduced performance in broadband operations.
Innovation Solution
The implementation of a gm3 cancellation technique using an auxiliary switching device in parallel with the main switching device, where the auxiliary device is biased to offset the gm3 component of the main device, effectively canceling gm3 over the range of LO amplitudes, thereby improving linearity and reducing third-order intermodulation distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single switching device is used in the active mixer circuit, then the device complexity is low, but the linearity deteriorates due to gm3 variations caused by LO amplitude variations
Solution Approach 1:
The single switching device is segmented into two parallel switching devices (first and second switching devices). Each device handles a portion of the signal, and their combined effect cancels the gm3 component that causes linearity degradation. This segmentation allows the mixer to maintain low linearity error while managing complexity through functional division.
Solution Approach 2:
The second switching device is configured to provide a counterbalancing effect to the gm3 variations of the first switching device. By biasing the second device appropriately, its gm3 component opposes and cancels the harmful gm3 variations from the first device, effectively counterweighting the linearity degradation that would occur with a single device.
2Adaptability or versatility
If the mixer operates over a wide range of LO amplitudes, then the adaptability is improved for broadband operations, but the measurement precision deteriorates due to third-order intermodulation distortion
Solution Approach 1:
The biasing configuration of the parallel switching devices is designed to dynamically compensate for gm3 variations across different LO amplitude ranges. As the LO amplitude varies during broadband operation, the combined gm3 response of the two devices remains relatively constant, maintaining signal conversion accuracy throughout the operating range. This dynamic compensation enables adaptable broadband operation without sacrificing measurement precision.
Data Source
AI summary
The present disclosure provides an apparatus that includes a first mixer circuit configured to convert between an RF signal and an IF signal based at least in part on an local oscillator (LO) signal. The first mixer circuit is electrically coupled to a first node that is configured to receive the LO signal and a first bias voltage, a second node that is configured to receive the RF signal or the IF signal, and a third node that is configured to provide the IF signal or the RF signal. The apparatus further includes a second mixer circuit electrically coupled to a fourth node configured to receive the LO signal and a second bias voltage, the second node, and the third node. The second bias voltage has a voltage level that is offset from the first bias voltage.