GaN Biasing Circuit Using FET Source Feedback for Yield Improvement
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Solution Overview
Problem
Gallium Nitride (GaN) MMICs require individual biasing at distinct gate bias voltages, leading to increased costs and complexity in assembly and testing due to the wide range of bias voltages needed, which traditional self-biasing techniques like resistor ladders cannot effectively accommodate, resulting in high failure rates and yield issues.
Innovation Solution
A biasing circuit using a positive voltage source and two reference FETs to generate a target bias voltage level, with a filtering capacitor and externally adjustable voltage level shifter, allowing for temperature compensation and improved thermal characteristics, enabling efficient biasing of GaN-based RF FETs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If traditional resistor ladder self-biasing techniques are used for GaN MMICs, then the biasing circuit is simple and occupies small area, but the wide range of bias voltages required cannot be accommodated, resulting in high failure rates and low yield
Solution Approach 1:
The biasing circuit uses a single resistor ladder structure that serves multiple functions: it provides bias voltage for multiple bond pads simultaneously, accommodates a wide range of bias voltage requirements (several volts) through its inherent voltage division ratio, and enables both testing and operation phases without requiring different circuit configurations. This multi-functional approach resolves the contradiction by maintaining circuit simplicity while achieving the versatility needed to handle wide bias voltage ranges.
Solution Approach 2:
The invention changes the electrical parameters of the biasing circuit by introducing a negative voltage source connected to selectable bond pads, which modifies the voltage division ratio dynamically. By selecting different bond pads during testing, the circuit can accommodate various bias voltage requirements (e.g., from 0V to several volts) without changing the physical circuit structure, thus resolving the contradiction between simple circuit design and ability to handle wide voltage ranges.
2Adaptability or versatility
If the number of bond pads and resistors is increased to accommodate the wide range of bias voltages required by GaN devices, then more bias voltage levels can be provided, but the device complexity and assembly cost increase significantly
Solution Approach 1:
A single resistor ladder structure with multiple bond pads serves the universal function of providing bias voltage for all GaN devices on the wafer. The same physical circuit is used for both testing (to determine required bias voltage) and for the actual biasing operation, eliminating the need for separate circuits or components. This resolves the contradiction by achieving wide voltage range coverage through parameter selection rather than through increasing component quantity.
Solution Approach 2:
The invention merges the testing function and the biasing function into a single integrated circuit structure. The bond pads that are used during testing to determine the required bias voltage are the same bond pads used during operation to apply the bias voltage. This merging eliminates the need for separate testing equipment and additional components, resolving the contradiction between versatility and complexity.
3Measurement precision
If discrete voltage steps of 0.2 volts are used in the resistor ladder, then precise bias voltage control is achieved for traditional semiconductors, but too many resistors and contact points are required for GaN devices with several volts bias range
Solution Approach 1:
The invention changes the effective voltage step size by dynamically selecting different bond pads during testing. Instead of using fixed 0.2V steps throughout, the testing process determines the appropriate voltage division ratio, and the same circuit is then used to provide the corresponding bias voltage. This parameter change approach resolves the contradiction by achieving the necessary voltage range coverage without requiring an excessive number of discrete components.
Data Source
AI summary
A wide bandgap voltage reference circuit generates a temperature stable negative bias reference voltage for use in wide bandgap circuits. The reference circuit uses field effect transistor (FET) based source feedback. It can also be used as source feedback in high power high bandgap device applications, where constant current is required over process and thermal variations.