Switchable GaN Bias Circuit for CMOS Control
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Solution Overview
Problem
Existing GaN HEMT amplifier technologies face challenges in setting quiescent bias conditions due to high supply voltages, which are not compatible with low voltage CMOS control circuitry, and require efficient switching between Class A, A/B, B, and standby biasing conditions while accommodating process variations.
Innovation Solution
A switchable current bias circuit using cascode configured MOS FET and GaN FET switches, combined with current source circuitry, allows low voltage CMOS control signals to set bias currents for GaN HEMTs, enabling switching between different biasing conditions by combining currents from multiple sources in response to digital control signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high voltage GaN HEMT devices are used for RF amplifier applications, then the amplifier can operate at high power and voltage levels, but the bias control circuitry cannot tolerate the high supply voltages
Solution Approach 1:
The bias control system is segmented into two independent voltage domains: a high voltage domain for the GaN HEMT power amplifier stage and a low voltage domain for the CMOS control circuitry. The high voltage bias circuitry is divided into multiple controllable current sources, each managed by low voltage CMOS switches, isolating the sensitive control elements from high voltage stress while maintaining power amplifier performance
Solution Approach 2:
A voltage level shifting interface is introduced as an intermediary between the low voltage CMOS control signals and the high voltage GaN HEMT bias network. This intermediary circuitry translates low voltage control signals into appropriate high voltage bias conditions, allowing the CMOS circuitry to control the high voltage amplifier without direct exposure to dangerous voltage levels
2Adaptability or versatility
If multiple biasing conditions are implemented for different amplification modes, then the amplifier can switch between Class A, A/B, B and standby modes, but the circuit complexity increases
Solution Approach 1:
The bias control system is segmented into multiple independent current source modules, where each module corresponds to a specific biasing condition (Class A, A/B, B, or standby). Each current source is controlled by dedicated CMOS switches, allowing independent selection and combination of bias currents to achieve different amplification modes without requiring a completely different circuit architecture for each mode
Solution Approach 2:
Multiple bias current sources are merged into a single unified bias network that can simultaneously or selectively provide different current levels to the GaN HEMT. The CMOS switch matrix combines multiple low-voltage control signals to generate the appropriate high-voltage bias condition, reducing overall system complexity compared to separate bias circuits for each operating mode
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
Enables precise control of bias currents for GaN HEMTs with high drain supply voltages, allowing the FETs to switch between Class A, A/B, B, and standby biasing conditions, effectively addressing the incompatibility between high supply voltages and low voltage control signals.
Implementation Method 1
a MOS FET and a GaN FET connected in a cascode configuration
Data Source
AI summary
A circuit having (A) a transistor; (B) a bias circuit for providing setting a bias current for the transistor, the bias current having a current level in accordance with a reference current fed to the bias circuit; and (C) a bias current level controller, comprising: (i) a plurality of switches, each one of the switches comprises: a MOS FET and a GaN FET connected in a cascode configuration; and (ii) current source circuitry, comprising a plurality of current sources, each one of the current sources being connected between a voltage source and a corresponding one of the plurality of switches, the current source circuit combining currents produced by the current source in response a binary control signal fed to a gate of the MOS FET, the combined current providing the reference current fed to the bias circuit.