Linear RSSI Circuit Using Degeneration Resistors for Low Power
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Solution Overview
Problem
Existing received signal strength indicators (RSSI) with linear characteristics often result in high circuit complexity, high power consumption, and large die area, which are undesirable.
Innovation Solution
A received signal strength indicator is designed with a simple configuration using a pair of input transistors with coupled emitters and base electrodes, where the input signal is differentially applied, and the signal strength indicator signal is obtained by taking the mean value of the differential signal referenced to a supply terminal, utilizing current sources and degeneration resistors to achieve a linear characteristic with reduced complexity and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If complex circuitry is used to achieve linear RSSI characteristic, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent changes the operating parameters of the transistor circuit by applying degeneration resistors to the emitter terminals and using specific biasing configurations. This transforms the inherently non-linear transistor characteristics into a linear relationship between input signal amplitude and output voltage, achieving accurate RSSI measurement without complex circuitry
Solution Approach 2:
The patent uses a current mirror configuration where a reference current is copied to multiple branches of the circuit. This copying mechanism allows the differential pair to produce accurate differential output signals that are proportional to the input signal amplitude, simplifying the overall circuit design while maintaining measurement precision
2Measurement precision
If complex circuitry is used to achieve linear RSSI characteristic, then measurement precision is improved, but power consumption increases
Solution Approach 1:
By modifying the circuit parameters through degeneration resistors and biasing schemes, the patent achieves linear operation in the active region of transistors. This allows the circuit to operate efficiently at lower current levels while maintaining measurement accuracy, reducing power consumption compared to complex alternative designs
3Measurement precision
If complex circuitry is used to achieve linear RSSI characteristic, then measurement precision is improved, but die area increases
Solution Approach 1:
The patent combines multiple functions into a single differential pair circuit configuration. The same transistors and resistors simultaneously provide signal differentialing, linearization, and output scaling functions. This merging of functions reduces the total component count and die area required compared to implementing these functions with separate complex circuits
4Device complexity
If simple configuration is used for RSSI, then device complexity is reduced, but measurement precision deteriorates
Solution Approach 1:
The patent achieves linear characteristic in a simple differential pair configuration by carefully selecting and adjusting circuit parameters such as degeneration resistor values, bias current levels, and transistor operating points. These parameter optimizations enable the simple circuit to produce accurate linear RSSI output without requiring complex additional circuitry
Data Source
AI summary
An RSS indicator with a linear characteristic that is of a simple configuration, low current consumption and small die area requirements, comprises a pair of input transistors with coupled emitters and base electrodes to which an input signal is differentially applied. Each of the input transistors has a collector load circuit connected between a first supply terminal and its collector, and a tail current sink connected between a second supply terminal and the coupled emitters. The load circuit of each input transistor includes a current source which supplies a current copied from the tail current. A signal strength indicator signal is obtained from a differential signal between corresponding output nodes of the collector load circuits by taking the mean value of the differential signal referenced to the first supply terminal.