DC-Coupled RF Modulator Biasing for Common-Mode Control

Solution Overview

Problem

Existing RF transmitters are sensitive to input common-mode voltages, leading to performance degradation, and rely on intermediate frequency amplifiers to mitigate this, which consume power and increase circuit area.

Innovation Solution

A modulator circuit that controls common-mode voltage without an intermediate frequency amplifier by generating a bias voltage as a sum of the desired common-mode voltage and the voltage drop across a load circuit, ensuring optimal common-mode voltage at the modulator input.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If intermediate frequency amplifiers are used to control common-mode voltage, then modulator performance is maintained, but power consumption increases and circuit area increases

Engineering Contradiction:

Improvemodulator performanceVSAvoidpower consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent removes the intermediate frequency amplifier from the signal path between DAC and modulator. Instead, it extracts only the essential function of common-mode voltage control by directly coupling the DAC output to the modulator input, eliminating the unnecessary amplification stage that consumed power and occupied area.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent merges the DAC output stage with the modulator input stage by directly coupling them. The load circuit at the DAC output is designed to provide the appropriate common-mode voltage level directly to the modulator, combining the functions of voltage level conversion and signal transmission in a single coupled interface.

Inventive Principle:

Principle #5Merging (Combining)

2Reliability

If intermediate frequency amplifiers are used to control common-mode voltage, then modulator performance is maintained, but circuit area increases

Engineering Contradiction:

Improvemodulator performanceVSAvoidcircuit area

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The patent removes the intermediate frequency amplifier from the signal path between DAC and modulator. Instead, it extracts only the essential function of common-mode voltage control by directly coupling the DAC output to the modulator input, eliminating the unnecessary amplification stage that consumed power and occupied area.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent merges the DAC output stage with the modulator input stage by directly coupling them. The load circuit at the DAC output is designed to provide the appropriate common-mode voltage level directly to the modulator, combining the functions of voltage level conversion and signal transmission in a single coupled interface.

Inventive Principle:

Principle #5Merging (Combining)

3Device complexity

If common-mode voltage is not controlled, then circuit complexity is reduced, but modulator performance degrades

Engineering Contradiction:

Improvecircuit complexityVSAvoidmodulator performance

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent applies preliminary action by designing the load circuit at the DAC output to pre-establish the correct common-mode voltage level before the signal enters the modulator. This preliminary voltage level setting ensures the modulator receives the proper common-mode voltage without requiring additional control circuits, maintaining performance while minimizing complexity.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS10720946B2DC coupled radio frequency modulator

Publication Date: 2020.07.21 TEXAS INSTRUMENTS INC

AI summary

A radio frequency transmitter includes a digital-to-analog converter (DAC), a load circuit, and a modulator circuit. The load circuit is coupled to an output of the DAC. The modulator circuit is coupled to the DAC and the load circuit. The modulator circuit includes a driver circuit configured to provide a bias voltage to the load circuit, and an amplifier configured to receive an output of the DAC biased by an output of the load circuit.