Cascode Variable-Gain Amplifier With Phase-Stable Gain Switching
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Solution Overview
Problem
Conventional variable-gain amplifiers (VGAs) in phased array systems fail to maintain constant phase and gain step consistency during gain switching, particularly in wide frequency bands, leading to deteriorated performance in 5G radio frequency front-end designs.
Innovation Solution
Incorporating a variable capacitor circuit that adjusts parasitic capacitance in the cascode circuit to maintain consistent output matching, ensuring constant phase and gain step across different frequencies during gain switching, using configurations such as varactor transistors, MOS transistors, or switches and capacitors to control capacitance values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If gain switching is implemented by controlling common-gate transistors in a cascode structure, then gain can be adjusted between high and low modes, but phase cannot be kept constant and gain step becomes inconsistent at different frequencies
Solution Approach 1:
The patent changes the electrical parameters (capacitance values) of capacitors in the cascode circuit based on the selected gain mode. When switching between high gain and low gain modes, different capacitor values are connected to adjust the parasitic capacitance of the common-gate transistors, thereby maintaining constant phase and consistent gain steps across different frequencies while enabling gain switching functionality
Solution Approach 2:
The patent applies preliminary compensation by pre-calculating and pre-configuring capacitor values that counteract the parasitic capacitance changes that would otherwise occur during gain switching. By selecting appropriate capacitor values before switching occurs, the circuit proactively prevents phase variation and gain step inconsistency, rather than correcting these issues after they arise
2Device complexity
If conventional VGA structures are used in wide frequency bands, then device complexity is reduced, but gain step consistency and phase stability deteriorate across the frequency band
Solution Approach 1:
The patent introduces multiple capacitors with different capacitance values that can be selectively connected based on the operating frequency and gain mode. This allows the parasitic capacitance of the common-gate transistors to be dynamically adjusted, maintaining gain step consistency and phase stability across wide frequency bands without significantly increasing circuit complexity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution ensures consistent gain step and phase performance across a wide frequency band, improving the overall performance of phased array systems by maintaining matching and reducing gain step differences between frequencies.
Implementation Method 1
a parasitic capacitance of the cascode circuit relative to the first node changes accordingly when viewed from the first node. However, a change in the parasitic capacitance causes a change in output matching of the VGA during gain switching
Implementation Method 2
the capacitance value of the variable capacitor circuit is adjusted to compensate for a change of the parasitic capacitance caused by the second amplification transistor array relative to the first node during gain switching. Therefore, before and after gain switching, the parasitic capacitance viewed from the first node remains approximately constant
Data Source
AI summary
A variable-gain amplifier and a phased array system are provided. A variable-gain amplifier includes a cascode circuit comprising a first amplification transistor and a second amplification transistor array that are cascaded, the second amplification transistor array comprising a plurality of second amplification transistors connected in parallel and configured to output an adjustable current to an output matching network, the first amplification transistor is a common-source transistor, the plurality of second amplification transistors are common-gate transistors, or the cascode circuit is a common-emitter common-base circuit, the first amplification transistor is a common-emitter amplification circuit, and the second amplification transistor array is a common-base amplification circuit. The variable-gain amplifier further including a variable capacitor circuit coupled to the second amplification transistor array and coupled to the output matching network at first nodes.