RF Power Detector Circuit With β-Independent Feedback
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Solution Overview
Problem
Power amplifiers in radiofrequency transmitters face significant output power variations due to process corners and temperature changes, making it challenging for conventional power detectors, especially those using CMOS transistors, to maintain constant output power, as they are affected by the non-ideal characteristics of diodes and variations in current gain (β).
Innovation Solution
A power detector system and method that utilize a transistor to measure the average bias and base voltage of an amplified signal, generating a power detector output signal independent of β by compensating for the effective diode voltage, allowing the output to correspond to the peak voltage level of the amplified signal, thereby reducing variations in output power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If power detectors are implemented using diodes, then the circuit can handle high signal levels, but non-ideal characteristics of diodes limit the ability to work over variations in process corners and temperature
Solution Approach 1:
The patent implements a feedback mechanism where the power detector output is fed back to the power amplifier to regulate output power. The feedback loop continuously monitors the output signal level and adjusts the amplifier gain to maintain constant output power despite variations in process corners and temperature, thereby resolving the reliability issue while maintaining high signal level handling capability
Solution Approach 2:
The patent changes the operating parameters of the power detector by using a transistor biased in a specific region and adjusting bias currents to compensate for diode non-ideal characteristics. By dynamically adjusting the bias conditions and operating point of the detector circuit, the patent maintains accurate power detection across varying process corners and temperature conditions while preserving the ability to handle high signal levels
2Device complexity
If conventional power detectors are used, then the circuit structure is simple, but output power variations cannot be effectively regulated
Solution Approach 1:
The patent introduces a feedback control loop that connects the power detector output back to the power amplifier input. This feedback mechanism automatically regulates the output power by adjusting the amplifier gain in response to detected power variations, achieving precise output power consistency without significantly increasing overall system complexity
Solution Approach 2:
The patent introduces an intermediary control circuit that processes the detector output signal and generates appropriate correction signals for the power amplifier. This intermediary stage translates the raw detector output into precise control signals that regulate output power, achieving manufacturing precision while maintaining relatively simple circuit architecture
Data Source
AI summary
Techniques are described for power detection of an amplified signal. For example, power detection described herein can receive an amplified signal from a power amplifier, and can generate an output signal that can be fed back to help regulate an output level of the power amplifier. Embodiments receive the amplified signal can be received by a transistor. A first measurement can be obtained at the transistor's emitter corresponding to an average bias level of the amplified signal, and a second measurement can be obtained at the transistor's base. The output signal can be generated as a function of a difference between the two measurements. Some embodiments further compensate for a measured effective diode voltage corresponding to a base-emitter voltage. Such an approach can generate the power detector output signal to be independent of the β of the transistor, and therefore less affected by variations in process corners and temperature.