Band-Pass Delta-Sigma ADC Feedforward Path for Higher S/N
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Solution Overview
Problem
The existing digital IF receivers with band pass ΔΣ modulators face challenges in achieving a good signal-to-noise (S/N) ratio due to high equivalent input noise, which is attributed to the dynamic range limitations of the quantizer and the resonator, leading to decreased accuracy and increased noise levels.
Innovation Solution
Incorporating a non-quadrature band pass ΔΣ modulator with a feedforward path that supplies the analog input signal directly to the quantizer, reducing the signal level fed into the resonator and allowing for increased gain and reduced noise, while also using a signal transmission circuit to mitigate spike noise effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the analog input signal is supplied directly to the resonator in a conventional band pass ΔΣ modulator, then the resonator processes the full signal level, but this causes high equivalent input noise and degraded S/N ratio due to dynamic range limitations
Solution Approach 1:
The patent segments the signal path into two separate paths: a feedforward path that supplies the analog input signal directly to the quantizer, and a feedback path that supplies only the quantization error signal to the resonator. This segmentation prevents the full signal level from entering the resonator, thereby reducing equivalent input noise and improving the S/N ratio while maintaining conversion accuracy.
2Measurement precision
If the signal level fed into the resonator is reduced, then equivalent input noise decreases, but the resonator gain must be increased to maintain signal integrity
Solution Approach 1:
The patent implements a feedback mechanism where the quantizer output is converted back to analog form by a D/A converter, and the difference between this reconstructed signal and the original analog input signal (i.e., the quantization error) is fed back to the resonator input. This feedback structure allows the resonator to operate with reduced signal levels while maintaining overall signal integrity through the closed-loop system.
3Device complexity
If a conventional band pass ΔΣ modulator structure is used, then the circuit is simpler, but the dynamic range limitations of the quantizer and resonator cause decreased accuracy
Solution Approach 1:
The patent introduces a D/A converter as an intermediary element between the quantizer and the resonator input. This intermediary converts the quantizer's digital output back to analog form, enabling the creation of a feedback path that supplies only the quantization error to the resonator. This intermediary component resolves the contradiction by allowing accurate error signal feedback without requiring the resonator to handle the full signal dynamic range.
Data Source
AI summary
The A/D converter converting an analog input signal into a digital output signal is constructed with a band pass ΔΣ modulator. The band pass ΔΣ modulator includes: a resonator showing a band-pass characteristic at a predetermined frequency and an attenuation characteristic at another frequency; a quantizer; and a local D/A converter. A signal of difference between the analog input signal and a local analog signal of the local D/A converter is supplied to the resonator. The A/D converter further includes an adder for supplying the analog input signal to an input of the quantizer. In addition, signal transmission circuits for reducing the influence of spike noise of the quantizer on the input to the resonator are connected between an input of the adder and an input of resonator selectively. The A/D converter constructed with the band pass ΔΣ modulator is improved in S/N ratio.