RF Power Control Circuit Using RAM Detection for Wide Dynamic Range
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Solution Overview
Problem
Conventional radio frequency power control circuits have a limited dynamic range of about 10 dB, which is insufficient for modern Digital Microwave Radio applications requiring adjustments over a wide range of more than 40 dB with high stability and accuracy, especially for automatic transmit power control and fade margin testing.
Innovation Solution
A radio frequency power control circuit incorporating a variable gain amplifier chain, an amplitude detector, a band pass filter, a logarithmic envelope detector, and a controller device with weighting coefficients to extend the dynamic range through residual amplitude modulation detection, allowing for precise control of the transmitter carrier level.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional amplitude detector with high coupling value is used to ensure stability at low signal levels, then detection stability is improved, but signal loss increases
Solution Approach 1:
The detection process is segmented into two parallel paths: one for detecting the carrier signal level and another for detecting the residual amplitude modulation. This segmentation allows each detector to be optimized for its specific function, with the RAM detector operating at lower coupling values since it detects modulated sidebands rather than the full carrier power.
Solution Approach 2:
The band-pass filter acts as an intermediary that selectively passes the residual amplitude modulation frequencies while blocking the carrier frequency. This allows the RAM detector to receive a filtered version of the signal that contains only the modulation information, enabling stable detection without requiring high coupling values.
2Device complexity
If conventional detection circuitry is used, then circuit simplicity is maintained, but dynamic range is limited to about 10 dB
Solution Approach 1:
The system dynamically adapts to different signal levels by using logarithmic amplification in the RAM detection path. The logarithmic amplifier compresses the wide dynamic range of the modulated signal into a manageable voltage range, enabling the detector to handle signals spanning more than 40 dB while maintaining linearity and accuracy.
Solution Approach 2:
The invention changes the detection parameter from direct amplitude detection to residual amplitude modulation detection. By detecting the envelope variations rather than the absolute amplitude, the system achieves extended dynamic range while using relatively simple circuit components.
3Measurement precision
If the transmitted carrier exceeds the diode threshold, then detection becomes possible, but low signal level detection becomes unstable
Solution Approach 1:
The system performs preliminary detection of the residual amplitude modulation before final power measurement. The band-pass filter and logarithmic amplifier prepare the modulated signal in advance, creating a stable detection reference that improves the reliability of low signal level measurements.
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 solution achieves a wide dynamic range of up to 50 dB, enabling accurate and stable power control over a broader range, effectively addressing the limitations of conventional circuits in modern DMR systems.
Implementation Method 1
an amplitude detector coupled to said variable gain amplifier chain
Implementation Method 2
the signal at the output of said band pass filter is provided to a logarithmic envelope detector
Data Source
Figure 1
AI summary
A radio frequency power control circuit comprising: a variable gain amplifier chain to provide a modulated radio frequency power; an amplitude detector coupled to said variable gain amplifier chain; a controller device receiving a detected signal from said amplitude detector and setting the gain of said variable gain amplifier chain; characterized in that said amplitude detector provides said detected signal to a band pass filter; the signal at the output of said band pass filter is provided to a logarithmic envelope detector; the signal at the output of said logarithmic envelope detector is coupled to an adder; the signal at the output of said amplitude detector is coupled to said adder; the signal at the output of said adder is coupled to said controller device.