Current-Mode Power Detector Using TDC for Low-Noise Signal Measurement
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Solution Overview
Problem
Voltage domain power detectors in wireless communication devices are limited in performance due to noise overwhelming lower power signals and higher power signals with high peak-to-average power ratio causing distortion, and large capacitors required for improvement occupy valuable space and increase settling time.
Innovation Solution
A current mode power detector that converts current to a clock signal with a frequency linearly related to current, using a time-to-digital converter (TDC) and analog-to-digital converter (ADC) to determine power, reducing complexity and space requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage domain power detection is used, then power detection function is provided, but performance is limited due to noise overwhelming lower power signals and distortion from higher power signals
Solution Approach 1:
The patent changes the detection domain from voltage to current. The power detector uses current mirrors to convert input voltage signals to current signals, then uses oscillators to convert currents to frequencies, and finally uses TDC to convert time intervals to digital values. This parameter transformation from voltage domain to current domain enables accurate detection of both low-power signals (without being overwhelmed by noise) and high-power signals (without causing distortion).
Solution Approach 2:
The patent replaces the traditional voltage-based detection mechanism with a current-based detection mechanism. Instead of directly measuring voltage and computing power, the system uses current mirrors to replicate and condition current signals, oscillators to frequency-modulate the currents, and TDC to digitally measure the time intervals. This substitution of detection mechanism fundamentally eliminates the noise and distortion issues inherent in voltage domain detection.
2Measurement precision
If large capacitors are used to improve voltage domain power detector performance, then detection accuracy improves, but device area increases and settling time increases
Solution Approach 1:
The patent changes the fundamental detection parameter from voltage to current, which eliminates the need for large capacitors. In the current domain, power detection is achieved through current mirrors and oscillators that naturally provide the necessary signal conditioning without requiring large energy storage elements. This parameter change simultaneously improves accuracy while reducing the detector area.
Solution Approach 2:
The patent substitutes the capacitor-based voltage detection mechanism with a current mirror-based detection mechanism. The current mirrors provide signal replication and conditioning, while oscillators provide frequency conversion, and TDC provides digital measurement. This substitution eliminates the need for large capacitors that would otherwise be required in voltage domain detectors to achieve comparable accuracy, thereby reducing both area and settling time.
3Ease of operation
If voltage domain power detection is used, then power detection is achieved, but modulation error and voltage headroom limitations occur
Solution Approach 1:
The patent transforms the detection from voltage domain to current domain, which eliminates voltage headroom limitations. In the current domain, the power detector can handle a wider dynamic range of input powers without encountering the voltage saturation issues that limit operational range in voltage domain detectors. The current mirrors and oscillators provide linear current-to-frequency conversion, reducing modulation errors and expanding the usable operational range.
Data Source
AI summary
A power detector includes a first current mirror that receives an input signal and generates a mirrored input signal, a first oscillator that reverses a first current of the mirrored input signal based on a voltage of the mirrored input signal reaching a threshold, and a first counter that generates a first count of each period generated by the first oscillator. The power detector also includes a second current mirror that receives a reference signal and generates a mirrored reference signal, a second oscillator that reverses a second current of the mirrored reference signal based on a voltage of the mirrored reference signal reaching the threshold, and a second counter that generates a second count of each period generated by the second oscillator. A processor then determine the power of the input signal based on the first count and the second count.