Active Mixer Load Commutation for Low Flicker Noise and Voltage Swing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing Gilbert-cell mixers face challenges with voltage headroom occupancy and flicker noise contribution in their load sections, which limit the available voltage swing and degrade the output signal quality, especially in direct-conversion receivers.
Innovation Solution
A mixer circuit with a load section utilizing commutative voltage-controlled current sources controlled by complementary logical signals, combined with a common-mode feedback circuit to minimize voltage headroom and modulate flicker noise out-of-band, reducing its impact on the output signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If resistors are used as load in Gilbert-cell mixer, then voltage-controlled current sources can be implemented, but considerable voltage headroom is occupied and voltage swing is limited
Solution Approach 1:
The patent changes the operating parameters of the load section by using voltage-controlled current sources instead of resistors, and by applying complementary logical signals to commutate the current sources. This allows the load to provide appropriate loading without occupying significant voltage headroom, thereby enabling greater voltage swing at the output.
2Length of stationary object
If voltage-controlled current sources are used as load, then voltage headroom is reduced, but flicker noise is generated and imposed on output signal
Solution Approach 1:
The patent converts the harmful flicker noise generated by the voltage-controlled current sources into an out-of-band noise by modulating it with complementary logical signals. The flicker noise that would normally degrade the output signal is instead shifted to frequencies away from the signal band, where it can be filtered out, thereby transforming a harmful effect into a manageable one.
Solution Approach 2:
The patent applies periodic complementary logical signals to commutate the voltage-controlled current sources in the load section. This periodic switching action modulates the flicker noise generated by the current sources, shifting it to out-of-band frequencies. The complementary nature of the signals ensures that the useful signal is preserved while the noise is moved to different frequency bands.
3Object-generated harmful factors
If commutative voltage-controlled current sources are used with complementary logical signals, then flicker noise is modulated out-of-band, but device complexity increases
Solution Approach 1:
The patent implements a load section where voltage-controlled current sources serve multiple functions: providing appropriate loading for the mixer core, enabling voltage swing without significant voltage headroom occupation, and generating modulated flicker noise that is shifted out-of-band. The complementary logical signals also serve dual purposes of commutating the current sources and modulating the noise, reducing the need for separate noise filtering circuits.
Data Source
AI summary
A low flicker noise active mixer comprises a trans-conductance section, a switching quad, and a load section. The trans-conductance section converts a voltage signal pair into a first current signal pair. The switching quad converts the first current signal pair into a second signal pair in a manner controlled by a LO (local oscillator) signal pair. The load section provides a loading to the second current signal pair using a pair of commutative active loads to convert the second current signal pair into an output voltage signal pair.