Nonlinear DAC Mixer Circuit for Transmitter Linearity

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Solution Overview

Problem

Mixer circuits in transmitters face challenges with non-linearities, requiring costly and complex pre-distortion circuits to compensate for these issues, which are inefficient and resource-intensive.

Innovation Solution

A mixer circuit with a digital to analogue converter having a non-linear transfer function, utilizing pairs of serially coupled switches and emitter coupled bipolar junction transistors to introduce non-linearity, simplifying compensation for non-linearities and reducing power consumption and chip size.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If pre-distortion circuits are used to compensate for non-linearities in power amplifiers, then the linearity of the transmitter is improved, but the device complexity and cost increase significantly

Engineering Contradiction:

Improvelinearity of transmitterVSAvoidcomplexity of pre-distortion circuit

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

Instead of using complex pre-distortion circuits to compensate for non-linearities, the patent inverts the approach by deliberately introducing non-linearities through a non-linear DAC. This non-linear DAC pre-distorts the signal in the opposite direction of the power amplifier's non-linearity, achieving linearization through a simpler, more cost-effective means while maintaining the desired linearity performance

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent changes the transfer function parameter of the DAC from linear to non-linear. By configuring the non-linear DAC with specific transfer characteristics that are inverse to the power amplifier's non-linearities, the system achieves compensation without requiring complex additional circuitry. This parameter change enables a simpler overall architecture while maintaining transmitter linearity

Inventive Principle:

Principle #35Parameter changes

2Ease of manufacture

If traditional linear DACs are used in mixer circuits, then the design is simpler, but compensation for non-linearities becomes costly and complicated

Engineering Contradiction:

Improvesimplicity of DAC designVSAvoidcomplexity of non-linearity compensation

Core Design Contradiction:

Ease of manufactureVSDevice complexity

Solution Approach 1:

The patent merges the function of non-linearity compensation directly into the DAC by making it non-linear. Instead of having a separate linear DAC and a separate pre-distortion circuit, the non-linear DAC combines both functions into a single component. This integration simplifies the overall mixer circuit design and reduces the number of separate components needed for compensation

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent converts the typically harmful non-linearities into a beneficial feature by deliberately designing the DAC to be non-linear. This non-linearity is not a defect but a deliberate characteristic used to pre-distort the signal and compensate for power amplifier non-linearities. By embracing non-linearity rather than fighting it, the patent achieves simpler compensation with reduced device complexity

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Reliability

If complex pre-distortion circuits are implemented, then non-linearity compensation is achieved, but power consumption and chip size increase

Engineering Contradiction:

Improvecompensation for non-linearitiesVSAvoidpower consumption of mixer circuit

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent extracts the non-linearity compensation function from complex separate circuits and embeds it directly within the DAC itself. By taking out the compensation functionality and integrating it into the existing DAC structure, the patent eliminates the need for additional dedicated compensation circuits, thereby reducing overall power consumption and chip area while maintaining effective non-linearity compensation

Inventive Principle:

Principle #2Taking out (Extraction)

Data Source

PatentUS9124215B2Mixer circuit

Publication Date: 2015.09.01 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

AI summary

A mixer circuit (200, 300, 800, 900) for mixing a first input signal at a first frequency with a second input signal at a second frequency to an output signal at a third frequency. The mixer circuit (200, 300, 800, 900) comprises a mixing stage (205, 805) with differential input ports (206, 207; 820, 821) for the first input signal and an input port (211, 911) for the second input signal and differential output ports for the output signal, which also serve as output ports for the mixer circuit. The mixer circuit (200, 300, 800, 900) comprises a nonlinear digital to analogue converter (210, 810) which has an input port (211) which is the input port for the second input signal and an output port (212) which is connected to the input port of the mixing stage, and the digital to analogue converter has a nonlinear transfer function.