Switched Resistor Network for Programmable Gain Mixer Circuits

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Solution Overview

Problem

Current resistor networks in passive current-mode mixer circuits face challenges in achieving accurate gain steps and maintaining a regulated input impedance, leading to suboptimal performance and increased noise figure due to parasitic input resistance and nonlinearity.

Innovation Solution

A resistor network topology with switched resistor branches connected between input and output terminals, incorporating a third resistor between input and output terminals, and using two switches per branch to maintain consistent input impedance across different gain settings, thereby improving linearity and accuracy.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If conventional resistor networks are used in passive current-mode mixer circuits, then the circuits can achieve basic gain adjustment, but the gain steps are inaccurate and the input impedance is not regulated due to parasitic input resistance and nonlinearity

Engineering Contradiction:

Improvegain step accuracyVSAvoidinput impedance regulation

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The resistor network is segmented into multiple parallel resistor branches, each with independently controllable switches. This segmentation allows selective activation of specific branches to achieve different gain settings while maintaining accurate gain steps and regulated input impedance by excluding parasitic effects from the active signal path.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Switches are introduced as intermediary elements to control the connection of individual resistor branches to the input terminal. These switches act as mediators that enable precise selection of resistor combinations, ensuring accurate gain steps and maintaining consistent input impedance across different gain settings by properly isolating parasitic input resistance.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If programmable gain is implemented with digital control, then gain can be adjusted in discrete steps, but the accuracy of gain steps deteriorates due to parasitic input resistance affecting the resistor network

Engineering Contradiction:

Improveprogrammable gain adjustmentVSAvoidgain step accuracy

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The resistor network is divided into multiple parallel branches with individually controllable switches, enabling digital control of gain while maintaining accuracy. Each branch can be independently activated or deactivated, allowing precise gain adjustment in discrete steps without the degradation caused by parasitic input resistance in conventional networks.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The resistor network transitions from a static configuration to a dynamic one where individual branches can be selectively activated or deactivated via switches. This dynamic reconfiguration enables programmable gain adjustment with high accuracy, as the active branches are properly isolated from parasitic input resistance effects.

Inventive Principle:

Principle #15Dynamics

3Adaptability or versatility

If R2R resistor networks are used for programmable gain, then gain adjustment is achievable, but the input impedance varies with different gain settings due to nonlinearity and parasitic resistance

Engineering Contradiction:

Improveprogrammable gainVSAvoidinput impedance consistency

Core Design Contradiction:

Adaptability or versatilityVSStability of the object's composition

Solution Approach 1:

The resistor network is segmented into multiple parallel branches with independent switch control, replacing the conventional R2R structure. This segmentation allows the input impedance to remain stable across different gain settings, as the switches properly isolate parasitic resistance and ensure consistent impedance presentation to the input terminal regardless of which branches are active.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The network topology is changed from a conventional R2R configuration to a parallel branch structure with controllable switches. This parameter change in the circuit architecture enables simultaneous achievement of programmable gain and stable input impedance, as the new structure allows independent control of gain while maintaining consistent impedance characteristics.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentEP3140912B1A resistor network and mixer circuits with programble gain

Publication Date: 2018.04.11 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

Figure 1(a)~1(c)
Figure 2~3
Figure 4

AI summary

A resistor network (300) comprises one or more switched resistor branches (311, 312). Each switched resistor branch comprises a first resistor (321 ) connected in series with a first switch (331 ), wherein a first terminal (301 ) of the first resistor (321 ) is connected to the input terminal (IN) of the resistor network (300), a second terminal of the first resistor (321 ) is connected to a first terminal of the first switch (331) forming a middle node (304), and a second terminal (302) of the first switch (331 ) is connected to the output terminal (OUT) of the resistor network (300). Each switched resistor branch further comprises a second resistor (322) connected in series with a second switch (332), wherein the series connected second resistor (322) and second switch (332) is connected between the middle node (304) and a third terminal (303) of the one or more switched resistor branches (311, 312). The resistor network (300) further comprises a third resistor (323) connected between the input and output terminals of the resistor network (300).