CT Delta-Sigma Modulator Capacitive Feed-Ins for STF Peaking

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Solution Overview

Problem

Continuous-time delta-sigma modulators (CTDSMs) face significant peaking in the Signal Transfer Function (STF) due to gigahertz sampling frequencies and excess loop delay, leading to out-of-band signal saturation and increased power consumption.

Innovation Solution

Implementing capacitive feed-ins to the integrator inputs of CTDSMs to shape the signal transfer function and reduce peaking, using capacitive feed-in coefficients to improve out-of-band gain and prevent signal components from reaching the integrator outputs.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If gigahertz sampling frequencies are used in CTDSMs, then the sampling rate is improved, but peaking in the Signal Transfer Function increases causing out-of-band signal saturation

Engineering Contradiction:

Improvesampling rateVSAvoidpeaking in Signal Transfer Function

Core Design Contradiction:

SpeedVSObject-affected harmful factors

Solution Approach 1:

The patent introduces capacitive feed-ins with specifically designed coefficients to modify the signal transfer function parameters. By adjusting the capacitive feed-in coefficients (Cf1, Cf2, Cf3), the STF is reshaped to reduce peaking while maintaining the gigahertz sampling rate, directly addressing the contradiction between high sampling rate and STF peaking

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

Capacitive feed-ins are introduced as intermediary elements between the input signal and the integrator inputs. These capacitors (Cf1, Cf2, Cf3) act as mediators that shape the signal transfer function before the signal reaches the integrators, thereby reducing peaking without affecting the sampling rate

Inventive Principle:

Principle #24Intermediary (Mediator)

2Stability of the object's composition

If excess loop delay is present in CTDSMs, then the loop stability is maintained, but peaking in the Signal Transfer Function increases

Engineering Contradiction:

Improveloop stabilityVSAvoidpeaking in Signal Transfer_function

Core Design Contradiction:

Stability of the object's compositionVSObject-affected harmful factors

Solution Approach 1:

The capacitive feed-in coefficients are specifically designed to compensate for the effects of excess loop delay. By adjusting these coefficients, the signal transfer function is reshaped to reduce peaking while maintaining loop stability, as the capacitive feed-ins modify the STF without affecting the noise transfer function or loop stability criteria

Inventive Principle:

Principle #35Parameter changes

3Manufacturing precision

If traditional resistive feed-ins are used, then the signal transfer function can be shaped, but large signal components reach the integrator outputs degrading linearity

Engineering Contradiction:

Improvesignal transfer function shapingVSAvoidlinearity

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The patent replaces resistive feed-ins with capacitive feed-ins. This substitution changes the feeding mechanism from resistive to capacitive, which fundamentally alters how signals are transferred to the integrators. The capacitive feed-ins shape the STF while preventing large signal components from reaching integrator outputs, thereby improving linearity while maintaining STF shaping capability

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

By changing from resistive to capacitive feed-ins, the patent modifies the electrical parameters of the feed-in network. The capacitive nature of the feed-ins changes the frequency response characteristics, allowing STF shaping while reducing the magnitude of signal components at integrator outputs, thus improving linearity

Inventive Principle:

Principle #35Parameter changes

4Power

If out-of-band gain is increased to handle interferers, then the signal transfer function peaking increases, but power consumption increases to overcome linearity degradation

Engineering Contradiction:

Improvepower consumptionVSAvoidout-of-band signal saturation

Core Design Contradiction:

PowerVSObject-affected harmful factors

Solution Approach 1:

The capacitive feed-in coefficients are optimized to reduce STF peaking while maintaining adequate out-of-band gain. By carefully selecting the values of Cf1, Cf2, and Cf3, the patent achieves a balance where out-of-band interferers are handled without excessive peaking, thereby reducing the power required by amplifiers to maintain linearity

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The capacitive feed-ins act as intermediary elements that preprocess the signal before it reaches the integrators. This preprocessing reduces the peaking in the STF, which in turn reduces the power consumption requirements of subsequent amplification stages while still maintaining the ability to handle out-of-band interferers

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS20260066918A1Continuous-Time Delta-Sigma Modulator with Capacitive Feed-ins

Publication Date: 2026.03.05 NXP BV

AI summary

In one or more embodiments, a continuous-time delta-sigma modulator (CTDSM) includes one or more integrators including one or more of a feed-forward loop or a feedback loop and including a one or more capacitive feed-ins to enable insertion of a signal at the outputs of the one or more integrators. The coefficients of one or more of the feed-forward loop, the feedback loop, or the capacitive feed-ins may be configured to shape a signal transfer function of the CTDSM. Additionally, the capacitive feed-ins remove signal components from the integrator outputs, reducing noise and reducing the power consumed by the CTDSM. In one or more embodiments, coefficients of the plurality of capacitive feed-ins may be selected to limit peaking in the signal transfer function (STF) of the CTDSM.