Power Amplifier Bias Circuit With Temperature-Compensated Preheating
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Solution Overview
Problem
Existing power amplifier circuits for fifth-generation mobile communication systems do not effectively consider the temperature-dependent variation of the hFE of transistors, which can lead to suboptimal modulation accuracy (EVM) across different environmental temperatures.
Innovation Solution
A power amplifier circuit that includes an amplifier transistor and a bias circuit with a temperature-compensating electrostatic capacity circuit. The bias circuit supplies a bias current to the amplifier transistor, with the electrostatic capacity circuit varying in accordance with the transistor's temperature and charging/discharging during supply and non-supply periods to optimize bias current delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a bias is transiently increased when power amplification is started, then the power amplification factor is transiently increased, but the full effect of improvement in modulation accuracy is not obtained in some environmental temperatures because temperature-dependent hFE variation is not considered
Solution Approach 1:
The patent applies parameter changes by varying the electrostatic capacity of the capacitor in the bias circuit according to temperature. The capacitor's electrostatic capacity is increased at lower temperatures and decreased at higher temperatures to compensate for hFE variations. This dynamic parameter adjustment ensures that the bias current effectively compensates for transistor gain changes across different environmental conditions, resolving the contradiction between achieving high modulation accuracy and maintaining temperature adaptability.
Solution Approach 2:
The patent implements feedback by using a temperature detection circuit to monitor the amplifier transistor's temperature and automatically adjust the capacitor's electrostatic capacity accordingly. The temperature detection signal feeds back to control the capacitor selection or variable capacitor value, creating a closed-loop system that maintains optimal bias conditions despite temperature variations, thereby achieving both high modulation accuracy and temperature adaptability.
2Productivity
If the electrostatic capacity circuit is charged in non-supply period and discharged in supply period, then the bias current delivery is optimized, but the circuit complexity increases
Solution Approach 1:
The patent applies periodic action by charging the electrostatic capacity circuit during the non-supply period (when no RF signal is present) and discharging it during the supply period (when RF amplification is active). This periodic charge-discharge cycle allows the capacitor to store energy when not needed and release it when bias current is required, optimizing the timing of bias delivery. This approach improves productivity by ensuring efficient bias current supply while keeping the circuit relatively simple by using standard capacitor charging/discharging mechanisms rather than complex active control systems.
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 proposed solution enables effective preheating of the amplifier transistor, shortening the time to thermal equilibrium and improving modulation accuracy (EVM) across varying temperatures, thus enhancing communication performance.
Implementation Method 1
an electrostatic capacity circuit whose electrostatic capacity varies in accordance with a temperature of the amplifier transistor
Implementation Method 2
a temperature compensation diode connected in series between a base of the bias current supply transistor and a reference potential
Implementation Method 3
a first thermistor whose resistance value varies in accordance with a temperature of the amplifier transistor
Data Source
AI summary
A power amplifier circuit includes an amplifier transistor that amplifies a radio-frequency signal and outputs the radio-frequency signal, and a bias circuit that supplies a bias current to a base of the amplifier transistor. The bias circuit includes a bias current supply transistor, and an electrostatic capacity circuit whose electrostatic capacity varies in accordance with a temperature of the amplifier transistor and that is charged in a non-supply period during which the bias current is not supplied and discharges to a supply path for the bias current in a supply period during which the bias current is supplied. The supply period during which the bias current is supplied includes an amplification period during which the radio-frequency signal is amplified by the amplifier transistor. The bias current starts to be supplied before the amplifier transistor starts amplification.