DC-Coupled RF Multi-Stage Amplifier Without AC Coupling Loss
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Solution Overview
Problem
Conventional RF amplifiers with AC coupling between gain stages suffer from parasitic capacitance, leading to reduced gain and increased power consumption due to the need for smaller tuning inductors and additional capacitance, which affects performance, especially in high-power on-chip amplifiers.
Innovation Solution
Implementing a multi-stage RF amplifier with DC coupling between gain stages, using alternating n-type and p-type transistors and bias transistors to eliminate parasitic capacitance and optimize gain, while saving silicon area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If AC coupling capacitors are used between gain stages, then gain stages can be independently biased, but parasitic capacitance is introduced which reduces amplifier gain
Solution Approach 1:
The patent removes the AC coupling capacitors from the signal path between gain stages. By directly connecting the drain of one gain stage transistor to the gate of the next gain stage transistor, the harmful parasitic capacitance of the coupling capacitors is eliminated, thereby maintaining high amplifier gain while still allowing independent biasing through separate biasing circuits connected to each gain stage.
Solution Approach 2:
The patent introduces separate biasing circuits as intermediary elements that provide independent DC bias voltages to each gain stage without interfering with the RF signal path. These biasing circuits use high-value resistors and current sources that have negligible effect on the RF signal while enabling independent control of each gain stage's operating point.
2Speed
If smaller tuning inductors are used to compensate for parasitic capacitance, then frequency tuning is achieved, but amplifier gain is reduced
Solution Approach 1:
By removing the AC coupling capacitors that introduce parasitic capacitance, the patent eliminates the need to use smaller tuning inductors to compensate for this capacitance. The direct DC coupling allows the use of larger tuning inductors that provide both the necessary frequency tuning and maintain high amplifier gain, as there is no parasitic capacitance to counteract.
3Ease of operation
If AC coupling capacitors are used, then gain stages are isolated, but significant silicon area is consumed
Solution Approach 1:
The patent eliminates the large AC coupling capacitors from the circuit by implementing direct DC coupling between gain stages. This removal of bulky capacitive components significantly reduces the silicon area occupied by the amplifier while maintaining proper gain stage isolation through separate biasing circuits and the natural high-impedance input of the following stage.
4Reliability
If extra power is consumed to satisfy gain requirements, then gain requirements are met, but power consumption increases
Solution Approach 1:
By removing the AC coupling capacitors and their associated parasitic capacitance, the patent eliminates the need to consume extra power to compensate for gain losses. The direct DC coupling preserves signal amplitude and gain throughout the amplifier stages, allowing the amplifier to meet gain requirements with normal power consumption levels.
Data Source
AI summary
An RF amplifier can include multiple gain stages, wherein each gain stage can be DC coupled to an adjacent gain stage. Each input gain stage can include either n-type gain transistors or p-type gain transistors. Multiple input gain stages can be designed/built by interleaving input gain stages of different types. Notably, an input gain stage including n-type gain transistors has a p-type bias transistor. Similarly, an input gain stage including p-type gain transistors has an n-type bias transistor. In this configuration, the bias transistor is the same type as the downstream gain transistors. Therefore, each bias transistor can accurately track the behavior of the transconductance devices of the next gain stage.