Variable-Gain Diode Detector Circuit for Accurate Transmit Power Sensing
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Solution Overview
Problem
The nonlinear response of microwave detector diodes in wireless local area network (WLAN) access points results in reduced transmit power precision at low output power levels, necessitating improved accuracy for applications like radio management and high-density pico cells.
Innovation Solution
A circuit comprising a diode detector followed by a series cascade of two operational amplifiers, where the second op amp has selectable gain factors, with a single control line configuring it for high or low gain, enhancing sensitivity and accuracy across a broader range of output power levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a detector diode is used with fixed gain amplification, then the circuit is simple, but the transmit power precision deteriorates at low output power levels
Solution Approach 1:
The patent implements dynamic gain adjustment in the amplifier circuit, switching between high gain and low gain modes based on the detected power level. The amplifier gain is dynamically changed to match the input signal strength, allowing precise measurement across a wide power range from -1 dBm to 20 dBm without requiring multiple fixed-gain amplifier circuits.
Solution Approach 2:
The patent changes the amplifier gain parameter adaptively based on the input signal level. By adjusting the gain parameter from high (for low power levels) to low (for high power levels), the system maintains optimal measurement precision across the entire power range while using a single amplifier circuit.
2Measurement precision
If multiple amplifier circuits with different gain factors are used, then the transmit power precision improves across all power levels, but the device complexity and PCB real estate increase
Solution Approach 1:
The patent makes a single amplifier circuit universal by enabling it to perform multiple measurement functions across different power levels through dynamic gain adjustment. The same amplifier circuit handles both low power (-1 dBm) and high power (20 dBm) measurements by switching its gain mode, eliminating the need for separate amplifier circuits for different power ranges.
Solution Approach 2:
The amplifier circuit dynamically switches between high gain and low gain modes based on the detected power level, allowing one circuit to replace multiple fixed-gain circuits. This dynamic adaptation reduces the number of physical amplifier circuits needed, thereby reducing PCB real estate requirements.
3Measurement precision
If the detector diode response is centered to fit the ADC window, then the circuit is simple, but the ALC accuracy deteriorates at low power levels due to the steep slope of the diode response
Solution Approach 1:
The patent uses the output of the variable gain amplifier as feedback to control the gain switching. The system continuously monitors the amplified signal level and adjusts the amplifier gain accordingly, creating a closed-loop control system that maintains optimal signal levels for ADC conversion across the entire power range, thereby improving ALC accuracy.
Solution Approach 2:
The control loop dynamically adjusts the amplifier gain based on the detected power level, preventing signal saturation at high power levels while ensuring sufficient signal strength at low power levels for accurate ADC conversion. This dynamic control improves ALC accuracy without requiring a completely redesigned detector diode response curve.
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
This solution provides improved transmit automatic level control (ALC) accuracy at low target power levels while minimizing circuit complexity and cost, maintaining precision at higher power levels with reduced PCB real estate requirements.
Implementation Method 1
The diode's output voltage is amplified and applied to an analog to digital converter (ADC)
Data Source
AI summary
A system and method for increasing accuracy of transmitter power detection over a larger range of output power levels wherein a diode detector is followed by a series cascade of 2 op amps. The first op amp functions as a differential/buffer amplifier, which improves temperature performance. The second op amp has two selectable gain factors. The output of the second op amp is routed to the ADC. A single control line is connected to a controllable switching device that configures the second op amp for high gain or low gain.