Discrete-Time Current Multiplier for Low-Noise FIR Filtering
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Solution Overview
Problem
Conventional finite impulse response (FIR) filters for radar systems suffer from noise, distortion, and high power consumption due to sample and hold blocks, coefficient multipliers, and digital-to-analog converters, making them inefficient for analog signal processing.
Innovation Solution
A programmable analog current multiplier with a transconductance stage and a multiplication stage that converts discrete time voltage to current, using current steering and digital control for linear signal division/multiplication, reducing noise and power consumption while increasing dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional FIR filter architecture with sample and hold blocks, coefficient multipliers, and voltage accumulators is used, then filtering function is achieved, but noise and distortion increase significantly
Solution Approach 1:
The patent replaces the conventional voltage-based FIR filter architecture with a current-based architecture. Sample and hold blocks are replaced by current sampling switches, coefficient multipliers by current mirrors with digital control, and voltage accumulators by current summing nodes. This substitution of the fundamental signal domain from voltage to current eliminates the need for noisy voltage accumulation and reduces distortion throughout the signal path.
Solution Approach 2:
The patent changes the fundamental parameter domain from voltage to current. By operating the entire FIR filter in the current domain, the system achieves linear signal addition through simple current summing at nodes, eliminating the need for voltage accumulators that introduce noise and distortion. The coefficient multiplication is achieved through current mirroring with digital control of mirror ratios, providing both accuracy and linearity.
2Measurement precision
If separate digital-to-analog converters are used for each coefficient multiplier, then filtering precision is improved, but power consumption increases
Solution Approach 1:
The patent merges the functions of multiple separate DACs into a single digital control mechanism that adjusts current mirror ratios. Instead of requiring N separate DACs for N coefficient multipliers, the system uses digital control signals to set the ratios of current mirrors, which are then multiplied by the input current. This consolidation dramatically reduces power consumption while maintaining precise coefficient control through the digital-to-analog conversion of only the ratio parameters rather than full coefficient values.
Solution Approach 2:
The current mirror structure serves multiple functions simultaneously: it provides coefficient multiplication, enables digital control of filter parameters, and achieves linear signal processing. By making the current mirror ratio programmable through digital control, a single hardware structure can implement multiple different filter coefficients without requiring separate conversion circuits for each, providing universal functionality across different filtering operations.
3Reliability
If conventional voltage-based FIR filter is used, then filtering operation is performed, but dynamic range is limited
Solution Approach 1:
The patent substitutes the voltage-based signal processing system with a current-based system. Current signals inherently provide better dynamic range because they can be summed linearly at nodes without the noise and distortion issues of voltage accumulation. The current mirrors provide precise gain control with high linearity, and the overall architecture achieves extended dynamic range through the linear current summing operation at the output node, eliminating the need for complex voltage accumulation circuits.
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
The solution achieves high dynamic range, low noise, and low power consumption, improving the performance and efficiency of FIR filters by using current signals for linear operations and eliminating the need for separate digital-to-analog converters.
Implementation Method 1
A programmable analog current multiplier with a transconductance stage and a multiplication stage that converts discrete time voltage to current
Implementation Method 2
using current steering and digital control for linear signal division/multiplication
Data Source
Figure 1~2B
Figure 3
Figure 4A~4B
AI summary
There is provided a programmable multiplier circuit for multiplying an input voltage signal by a binary coefficient, the multiplier circuit including a transconductor including a first amplifying transistor configured to convert the input voltage signal to a current signal, the first amplifying transistor having a gate configured to receive the input voltage signal, and a coefficient multiplier coupled to the transconductor and configured to multiply the current signal by the binary coefficient to generate an amplified current signal.