Low Noise Amplifier Input Resistance Compensation
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Solution Overview
Problem
Existing low noise amplifiers face challenges in maintaining a constant input resistance and linearity across varying signal levels, particularly in urban areas where satellite signal transmission and reception are limited, and they struggle to reduce gain effectively without degrading the signal-to-noise ratio.
Innovation Solution
A low noise amplifier design featuring a first circuit block capable of amplifying voltage signals, a feedback network, and a second circuit block that compensates for variations in resistance to maintain constant input resistance, utilizing bipolar or MOS transistors and variable resistors to adjust gain and ensure good linearity at high and low signal levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If gain is reduced when input signal power increases to avoid saturation, then linearity is improved, but input coupling deteriorates due to standing waves
Solution Approach 1:
The patent implements a feedback network that senses the input signal and adjusts the amplifier gain accordingly. When the input signal power increases, the feedback mechanism automatically reduces the gain to prevent saturation and maintain linearity, while preserving good input coupling characteristics across the entire operating range.
Solution Approach 2:
The amplifier employs dynamic gain control where the gain is not fixed but varies automatically based on the input signal level. This dynamic adjustment allows the amplifier to maintain optimal performance for both weak signals (high gain) and strong signals (low gain), resolving the contradiction between linearity and input coupling.
2Reliability
If variable resistance is used to reduce gain, then linearity improves at high signal levels, but input resistance becomes non-constant
Solution Approach 1:
The patent introduces a compensation circuit as an intermediary element that counteracts the variations in input resistance caused by the variable resistance used for gain control. This compensation mechanism ensures that the overall input resistance remains substantially constant while still allowing the gain to vary for maintaining linearity at different signal levels.
3Reliability
If amplifier gain is reduced to handle weak signals, then noise pattern improves, but gain reduction is limited by resistor ratios
Solution Approach 1:
The patent utilizes parameter changes in the active circuit elements (transistors) to achieve a wider gain variation range than what is possible with passive resistor ratios alone. By dynamically changing the operating parameters of the active devices, the amplifier can achieve the required gain reduction for noise optimization while maintaining the ability to handle both weak and strong signals effectively.
Data Source
AI summary
A low noise amplifier is provided that includes a first circuit block capable of amplifying a first voltage signal that is input to the amplifier. The first circuit block includes a first terminal coupled to a first supply voltage by a variable resistance, and a second terminal coupled to a second supply voltage. The second terminal is coupled to an output terminal of the amplifier, and the first voltage signal is applied to a further terminal of the first circuit block. The amplifier also includes a feedback network coupled to the output terminal and to the further terminal of the first circuit block, and a second circuit block coupled between the second supply voltage and the further terminal of the first circuit block. The second circuit block is adapted to compensate for variations in value of the variable resistance to ensure a substantially constant input resistance of the amplifier.