Programmable IF Receiver Using Double-Quadrature Harmonic Rejection
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Solution Overview
Problem
Existing RF receiver architectures, such as the superheterodyne and direct conversion methods, face challenges in image rejection due to sensitivity to I-Q mismatches and harmonic issues, particularly with the Hartley architecture being sensitive to gain and phase imbalances caused by temperature and process variations.
Innovation Solution
A tunable receiver system utilizing a programmable IF PLL and polyphase filters, which can be configured as lowpass or bandpass filters, integrated with double-quadrature down- and up-converters to minimize harmonic parasitic tuning and achieve high image rejection ratios, using active R-C polyphase filters with programmable center frequency and bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the Hartley architecture is used for image rejection, then image rejection capability is improved, but sensitivity to I-Q mismatches due to temperature and process variations worsens
Solution Approach 1:
The patent implements a feedback mechanism where the image rejection performance is continuously monitored and the I-Q mismatch parameters are adjusted accordingly. This closed-loop system compensates for temperature and process variations by detecting image leakage and dynamically correcting the quadrature balance, thereby maintaining high image rejection capability while reducing sensitivity to environmental changes.
Solution Approach 2:
The patent employs variable resistors and capacitors that can change their electrical parameters in response to temperature and process variations. By dynamically adjusting these passive components, the system maintains optimal I-Q matching conditions across different operating conditions, resolving the contradiction between achieving high image rejection and maintaining reliability against environmental changes.
2Device complexity
If direct conversion architecture is used to eliminate IF stage, then component count is reduced, but second mixer stage requires external components to preserve image rejection properties
Solution Approach 1:
The patent merges the image rejection function with the second mixer stage by integrating polyphase filters directly into the mixer circuitry. This consolidation eliminates the need for separate external image rejection components while preserving the image rejection properties, thereby reducing overall device complexity without compromising ease of manufacture.
Solution Approach 2:
The second mixer stage is designed to perform multiple functions simultaneously: frequency conversion and image rejection. By incorporating programmable polyphase filters that can be configured for different image rejection modes, the mixer becomes a universal component that handles both signal conversion and spectral purification, eliminating the need for dedicated external image rejection components.
3Adaptability or versatility
If programmable polyphase filters are used with configurable lowpass or bandpass modes, then adaptability to different TV systems is improved, but filter complexity increases
Solution Approach 1:
The patent implements dynamically reconfigurable polyphase filters where the filter characteristics (lowpass or bandpass mode, center frequency, bandwidth) can be changed in real-time through digital control. This dynamic reconfiguration capability allows the same filter hardware to adapt to different TV system standards and channel spacings without requiring multiple dedicated filter circuits, thereby achieving high versatility while managing complexity through time-multiplexed functionality.
Data Source
AI summary
A tuner system for receiving a plurality of frequency bands includes a low noise amplifier coupled with a band selection filter to select a desired band. The tuner system further includes a complex RF filter to produce a complex RF signal from the selected band. The tuner system includes two double-quadrature converters, the first double-quadrature converter frequency down-converts the complex RF signal to a complex baseband signal. The complex baseband signal passes through a baseband filter that contains two identical lowpass filters for obtaining a baseband in-phase (I) signal and a quadrature (Q) signal. The second double-quadrature converter up-converts the baseband I and Q signals to respective IF I and Q signals that are significantly free of the positive third IF harmonic. The third IF-harmonic free I and Q signals are further processed by a complex bandpass filter. The bandpass filter has a programmable frequency center and a programmable bandwidth.