Dual-Use RF Transistor Cascode Without External Switches
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Solution Overview
Problem
Existing RF communication device circuits face challenges in minimizing parasitic capacitance and impedance matching at high frequencies, especially above 3 GHz, due to the use of external switches and filters, which degrades sensitivity and increases power consumption, and are unsuitable for ultra-wideband transceivers and deep-submicron processes.
Innovation Solution
A circuit design featuring a common-gate amplifier configuration with a choke for voltage biasing, allowing the circuit to operate in receive and transmit modes without external switches, using a common amplifier that forms a low noise amplifier in receive mode and a power amplifier in transmit mode, with adjustable gate voltage for impedance matching and amplitude modulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If external switches are used to couple antenna to transmit and receive circuitry, then the circuit can be switched between transmit and receive modes, but parasitic capacitance increases and insertion losses degrade sensitivity
Solution Approach 1:
The patent removes external switches from the signal path and integrates the switching function directly into the amplifier circuitry. The amplifier's input stage inherently provides the switching mechanism through its transistor gates, eliminating the need for separate external switch components and their associated parasitic capacitances.
Solution Approach 2:
The patent combines the amplifier and switch functions into a single integrated circuit block. The same amplifier that provides signal amplification also performs the switching between transmit and receive modes through controlled transistor operation, merging two previously separate functions into one unified component.
2Reliability
If external filters and switches are used in the signal path, then transmit and receive modes can be isolated, but component count increases and PCB area is consumed
Solution Approach 1:
The patent merges the filter, amplifier, and switch functions into a single integrated circuit block. The low-pass filter is implemented as an integrated circuit rather than discrete components, and the switching function is built into the amplifier's control logic, dramatically reducing the total component count while maintaining mode isolation.
Solution Approach 2:
The integrated circuit performs multiple functions simultaneously: filtering, amplification, switching, and impedance matching. This multi-functional approach eliminates the need for separate dedicated components for each function, reducing overall device complexity while maintaining all necessary operations.
3Manufacturing precision
If conventional circuits are used with deep-submicron processes, then manufacturing precision is improved, but voltage swing stresses low-signal devices in receive path
Solution Approach 1:
The patent segments the signal path into distinct transmit and receive sections with separate power supply domains. The receive path operates from a lower voltage domain (1.2V) while the transmit path can operate from a higher voltage domain (1.8V), isolating low-signal receive devices from the high voltage swings of transmit operations.
Solution Approach 2:
The patent changes the voltage parameter across different operational modes and circuit sections. By using different supply voltages for receive and transmit paths, and dynamically adjusting bias voltages during mode transitions, the circuit protects sensitive receive devices from transmit-level voltage stress while maintaining optimal performance in each mode.
Data Source
Figure 1~2
Figure 3
AI summary
A circuit for amplifying radio frequency signals comprising: a terminal for connection to an antenna; a common amplifier arranged in a common-gate configuration between a first node and said terminal; a transmit amplifier operable to amplify a radio frequency signal present at an input node and provide the amplified signal to said first node; and a receive amplifier operable to amplify a radio frequency signal present at said first node and provide the amplified signal to an output node; wherein the circuit is operable in two modes: in a receive mode, the common and receive amplifiers being configured so as to together form a receive cascode for amplifying radio frequency signals received at the terminal; and in a transmit mode, the common and transmit amplifiers being configured so as to together form a transmit cascode for amplifying radio frequency signals applied at the input node.