FDNR Gain Filter Topology for Low-Noise Blocker Rejection
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Solution Overview
Problem
Existing electrical filtering technologies face challenges with noise performance, requiring higher power and chip area due to noise contribution from active and passive components in the signal path, and a trade-off between linearity and noise performance in receiver design, especially in wireless receivers where filtering must be performed at baseband.
Innovation Solution
A noise shaping and voltage gain filtering electrical circuit using a Frequency Dependent Negative Resistance (FDNR) circuit positioned only in the signal blocker path, with a capacitor in parallel to high-pass filter noise out of the signal band, allowing amplification without noise contribution from the filter, and employing multiple cascading transconductance stages for improved SNR control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If filter stages are placed in the signal path before amplification, then linearity requirements are reduced, but noise performance deteriorates because filter components contribute noise to the signal
Solution Approach 1:
The circuit segments the signal path into in-band signal path and out-of-band blocker path. The filter is placed only in the blocker path, separating filtering function from the main signal amplification path, thereby preventing filter noise from contaminating the signal while still achieving linearity improvement through blocker rejection
Solution Approach 2:
The patent introduces an intermediary frequency-dependent negative resistance (FDNR) filter that selectively affects different frequency bands. The FDNR acts as a mediator that creates short circuits for out-of-band blockers while maintaining high impedance for in-band signals, enabling noiseless filtering for the desired signal
2Object-affected harmful factors
If amplification is performed before filtering, then noise performance is improved by amplifying the signal first, but linearity requirements on the amplifier increase significantly
Solution Approach 1:
The circuit performs preliminary action by pre-filtering out-of-band blockers before they reach the amplifier. The FDNR filter is configured to create short circuits for out-of-band signals at the amplifier input, removing harmful blockers in advance and thereby relaxing the linearity requirements on the subsequent amplifier stage
3Measurement precision
If higher order filters are used to improve selectivity, then filtering performance is improved, but noise contribution from filter components increases
Solution Approach 1:
The higher order filter is segmented such that only the blocker-rejection function is implemented, while the signal path remains clean. The FDNR-based filter structure provides higher order out-of-band rejection through cascaded stages without placing noisy passive components in the in-band signal path, thus achieving improved selectivity without proportional noise increase
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach minimizes chip area and power consumption by isolating noise outside the signal band, relaxing linearity requirements on amplifiers, and reducing DC offsets and mismatches, enabling high dynamic range filters with low noise and selectivity.
Implementation Method 1
A noise shaping and voltage gain filtering electrical circuit using a Frequency Dependent Negative Resistance (FDNR) circuit positioned only in the signal blocker path
Implementation Method 2
with a capacitor in parallel to high-pass filter noise out of the signal band
Data Source
AI summary
A noise shaping and voltage gain filtering third order electrical circuit and method comprises at least one pair of input resistors; a Frequency Dependent Negative Resistance (FDNR) filter positioned in between the at least one pair of input resistors; a feedback resistor; and an amplifier operatively connected to the feedback resistor and the at least one pair of input resistors, wherein as an electrical signal is introduced to the electrical circuit, the FDNR filter is adapted to filter signal blockers out of the electrical signal prior to the electrical signal reaching the amplifier for signal amplification, wherein the FDNR filter does not contribute noise to a signal-to-noise ratio (SNR) of the electrical signal, and wherein a transfer function of the FDNR filter is substantially elliptical in shape.