RF Digital-to-Analog Conversion With Lower Phase Noise

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Solution Overview

Problem

Wireless apparatuses, such as cellular mobile phones, face challenges with high phase noise and poor signal quality due to the digital to analog conversion process, particularly when using sigma-delta modulation, which affects the efficiency of radiofrequency transposition signals.

Innovation Solution

A radiofrequency digital to analog converter (RF DAC) is developed that combines digital signals with radiofrequency transposition signals, generating a modulated analog signal with controlled power, and incorporates a notch filter to reduce quantization noise, allowing for easier integration into advanced CMOS technologies and operation with multiple radio systems without the need for special RF or analog components.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a high frequency sigma-delta modulator is used to reduce the number of bits in the digital to analog conversion stage, then the device complexity is reduced, but the phase noise increases and signal quality deteriorates

Engineering Contradiction:

Improvenumber of bits in digital to analog conversion stageVSAvoidphase noise and signal quality

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent divides the single high-order sigma-delta modulator into multiple parallel first-order sigma-delta modulators. Each modulator operates independently at a lower order, reducing individual phase noise contributions. The segmented architecture maintains the overall bit reduction goal while improving signal quality through distributed processing.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent implements a nested structure where multiple first-order sigma-delta modulators are embedded within a unified digital to analog conversion framework. The parallel modulators are nested within a common control and synthesis architecture that coordinates their outputs to achieve the desired signal reconstruction with reduced phase noise.

Inventive Principle:

Principle #7Nested doll (Nesting)

2Device complexity

If frequency division is used to obtain radiofrequency transposition signals, then the device complexity is reduced, but the phase noise increases and transposed signal quality deteriorates

Engineering Contradiction:

Improveradiofrequency signal generation methodVSAvoidphase noise and transposed signal quality

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

Instead of using traditional frequency division to generate radiofrequency transposition signals, the patent inverts the approach by using direct digital synthesis and digital to analog conversion of modulated signals. This reverses the conventional signal generation pathway, avoiding the phase noise issues associated with frequency division while maintaining device simplicity.

Inventive Principle:

Principle #13The other way round (Inversion)

3Reliability

If analog RF solutions are used for digital to analog conversion, then the signal quality is maintained, but the silicon area increases and integration difficulty increases

Engineering Contradiction:

Improvesignal qualityVSAvoidsilicon area

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The patent replaces analog RF circuitry with digital signal processing and digital to analog conversion architecture. By substituting mechanical/analog components with digital equivalents, the system maintains signal quality through precise digital control while dramatically reducing silicon area and enabling standard CMOS integration.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the operating parameters from analog domain to digital domain, using digital modulation and digital to analog conversion. This parameter transformation allows the system to achieve analog-like signal quality with digital precision while reducing the physical footprint and integration complexity associated with analog RF components.

Inventive Principle:

Principle #35Parameter changes

4Ease of operation

If analog base band circuitry is used, then the signal processing capability is provided, but the nonlinearities and noises from analog filters and mixers are introduced

Engineering Contradiction:

Improvesignal processing capabilityVSAvoidnonlinearities and noises

Core Design Contradiction:

Ease of operationVSObject-generated harmful factors

Solution Approach 1:

The patent substitutes analog base band circuitry including filters and mixers with digital signal processing architecture. This replacement eliminates the nonlinearities and noise generation inherent in analog components while preserving full signal processing capability through digital algorithms and computational methods.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS7755524B2Method for performing a digital to analog conversion of a digital signal, and corresponding electronic device

Publication Date: 2010.07.13 STMICROELECTRONICS INT NV

AI summary

A method for processing a digital signal includes an elementary processing including a radiofrequency transposition with a radiofrequency transposition signal and a digital to analog conversion of the transposed digital signal for delivering a radiofrequency analog signal. The digital to analog conversion is controlled by a control signal and a power control signal, the control signal having a frequency twice the frequency of the radiofrequency transposition signal. Each transition of the radiofrequency transposition signal occurs between two consecutive pulses of said control signal.