Cascode Amplifier Isolation Using a Shunt Ground Path
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Solution Overview
Problem
Existing wireless communication device amplifiers face performance degradation due to signal leakage when an amplifier is disabled, which compromises isolation and affects overall system performance.
Innovation Solution
The implementation of a cascode circuit with a shunt path to ground in amplifiers, which includes multiple cascode transistors in series for signal passing and a shunt transistor to provide improved isolation when the amplifier is disabled, effectively blocking signal leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an amplifier is disabled to save power or manage signal flow, then power consumption is reduced and signal flow is managed, but signal leakage occurs through the disabled amplifier causing poor isolation
Solution Approach 1:
A shunt transistor is introduced as an intermediary component connected between the cascode circuit output node and ground. This shunt transistor acts as a mediator that provides an alternative path for leaked signals to reach ground instead of propagating through the disabled amplifier, thereby improving isolation without requiring changes to the main amplifier signal path
Solution Approach 2:
The harmful signal leakage path is extracted and redirected to ground through the shunt transistor. By separating the leakage current from the main signal path and directing it to ground, the harmful effect of signal leakage is removed from the system while the main amplifier function remains intact
2Reliability
If a simple switch is used to disable the amplifier, then device complexity is reduced and ease of operation is improved, but isolation performance deteriorates due to signal leakage
Solution Approach 1:
The shunt transistor is merged with the existing cascode amplifier structure, sharing the same control signal and operating in parallel with the main amplification path. This integration adds minimal complexity while achieving significant isolation improvement, as the shunt transistor becomes a natural part of the amplifier circuit rather than a separate isolation component
Solution Approach 2:
The shunt transistor is made dynamically controllable through the same control signal that enables/disables the main amplifier. When the amplifier is disabled, the shunt transistor automatically activates to provide the ground path for leakage currents, and when the amplifier is enabled, the shunt transistor deactivates to avoid interfering with the signal path, providing adaptive isolation without manual intervention
Data Source
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AI summary
Amplifiers with improved isolation are disclosed. In an exemplary design, an apparatus (e.g., a wireless device, an integrated circuit, etc.) includes an amplifier (500) having a gain transistor(514), first and second cascode transistors (513,515), and a shunt transistor (517). The gain transistor receives an input signal (RFin) and provides an amplified signal. The first cascode transistor is coupled between the gain transistor and an intermediate node (X) and receives the amplified signal. The second cascode transistor is coupled between the intermediate node and an output node and provides an output signal (RFout). The shunt transistor is coupled between the intermediate node and circuit ground. The first and second cascode transistors are enabled to provide the output signal. The shunt transistor is (i) disabled when the cascode transistors are enabled and (ii) enabled to short the intermediate node to circuit ground when the cascode transistors are disabled.