Power Amplifier Bias Circuit for Power Density Matching
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Power amplifiers in RF applications face challenges in maintaining linearity and power density matching between bias circuitry and PA transistors due to different voltage supply levels, leading to non-linear variations in gain and error vector magnitude (EVM) degradation.
Innovation Solution
A bias circuit with a reference device and a differential amplifier, connected to a power density matching circuit, which includes a current translator circuit using transistors sized to match current densities between the reference and amplifier devices, ensuring power density alignment across different voltage supply levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the bias circuitry operates using a lower voltage supply than the PA transistor to reduce power consumption, then power consumption is reduced, but power density matching between bias circuitry and PA transistor deteriorates
Solution Approach 1:
A power density matching circuit is introduced as an intermediary between the bias circuitry and the PA transistor. This circuit includes a first portion connected to the bias circuitry and a second portion connected to the PA transistor, with a gain element that provides different gain for signals at different frequencies. The gain element is configured to provide higher gain for higher frequencies, which compensates for the power density mismatch caused by different voltage supply levels, thereby maintaining accurate bias conditions while allowing different voltage supplies.
Solution Approach 2:
The power density matching circuit employs a dynamic gain element that adjusts its gain based on signal frequency. The gain element provides frequency-dependent gain adjustment, offering higher gain for higher frequency signals and lower gain for lower frequency signals. This dynamic adjustment enables the circuit to maintain power density matching across varying operating conditions while allowing the bias circuitry to operate at lower voltage levels.
2Use of energy by moving object
If the PA and bias circuitry are switched from off-state to on-state on demand to reduce power consumption, then power consumption is reduced, but linearity deteriorates due to non-linear temperature changes
Solution Approach 1:
The power density matching circuit acts as a mediator that compensates for temperature-induced non-linearities. When the PA transistor is switched on, temperature changes cause parameter variations that would normally degrade linearity. The frequency-dependent gain element in the power density matching circuit dynamically adjusts to compensate for these changes, maintaining linear operation even during transient on-state transitions.
3Use of energy by moving object
If different voltage supply levels are provided to bias circuitry and PA transistor, then power consumption is reduced, but gain stability deteriorates due to non-linear temperature variations
Solution Approach 1:
The gain element in the power density matching circuit provides dynamic, frequency-dependent gain adjustment that compensates for temperature variations. As temperature changes occur due to different voltage supply levels, the gain element automatically adjusts its characteristics to maintain stable gain across the operating range, ensuring consistent performance despite the voltage difference between bias circuitry and PA transistor.
Data Source
AI summary
Circuits and methods related to power amplifiers. In some implementations, a bias circuit includes a reference device connectable to receive a first electrical supply level, the reference device arranged to produce an electrical bias condition using the first electrical supply level, and the reference device connectable to provide the electrical bias condition to an amplifier device connectable to a second electrical supply level. The bias circuit also includes a differential amplifier connectable to receive the first electrical supply level, the differential amplifier having a first input connectable to a first node of the reference device and a second input connectable to receive a reference electrical level, the differential amplifier arranged to maintain a first electrical level on the first node of the reference device as a function of the reference electrical level.