Multi-Stage RF Amplifier Topology for Low 1/F Mixer Noise
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Solution Overview
Problem
RF amplifiers in mixers face challenges with 1/f noise generation due to MOS switches, which increases with decreasing chip technology sizes, and passive mixers reduce noise but increase power dissipation with higher current gain stages.
Innovation Solution
The RF amplifier design includes two amplifying circuits with stages connected in series, each comprising a transistor and a resistor or current source, with summation nodes to combine amplified signals, ensuring symmetry and reducing noise while managing power dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If MOS switches are used in the mixer to steer signals and DC, then the mixer can be compact and integrated, but 1/f noise increases with decreasing chip technology sizes
Solution Approach 1:
The patent extracts the bias current path from the switch nodes by using separate bias current sources for the gain stages. This separates the harmful 1/f noise generation (which occurs at switch transitions) from the signal path, allowing the switches to operate without carrying DC bias current that would generate 1/f noise during transitions.
Solution Approach 2:
The patent introduces operational amplifiers as intermediary elements that buffer the bias current from the gain stages. These op-amps act as mediators that prevent the bias current from flowing through the switching nodes, thereby eliminating the generation of 1/f noise at the mixer output while still allowing the switches to perform their signal steering function.
2Object-generated harmful factors
If the bias current of the preceding gain stage is increased to reduce 1/f noise, then the noise figure of the mixer improves, but the power dissipation in the mixer increases
Solution Approach 1:
The patent extracts the bias current path from the signal path by using separate current sources. The bias current for the gain stages is provided through dedicated current mirrors that do not flow through the switching nodes, thereby reducing 1/f noise without requiring increased current that would raise power dissipation.
Solution Approach 2:
The patent changes the operating parameters by using operational amplifiers to buffer and regulate the bias current. This allows the gain stages to operate at optimized current levels that minimize 1/f noise without the need to increase current to excessive levels, thereby controlling power dissipation while achieving low noise performance.
Data Source
AI summary
An RF amplifier for amplifying a composite RF signal includes a first RF signal and a second RF signal. The amplifier includes a first amplifying stage for providing a first amplified signal a second amplifying stage for providing a second amplified signal, a third amplifying stage for providing a third amplified signal and a fourth amplifying stage for providing a fourth amplified signal, the fourth amplifying stage being arranged after the third amplifying stage. The respective amplified signals are summed up to obtain amplified RF signals.