CMOS Power Detectors

July 18, 2023

Cadence PCB Solutions

Key Takeaways

A CMOS power detector measures the power level of a radio frequency (RF) signal using complementary metal-oxide-semiconductor (CMOS) technology.
CMOS power detectors offer several advantages, including low power consumption, compact size, and compatibility with CMOS technology.
CMOS power detectors are widely used in wireless communication systems, including cellular networks, WiFi, Bluetooth, and other RF-based applications.

CMOS power detector

A CMOS power detector measures the power level of a radio frequency (RF) signal using complementary metal-oxide-semiconductor (CMOS) technology. Many wireless communication systems and RF integrated circuits (RFICs) use them for power control, signal monitoring, and automatic gain control.

A CMOS power detector measures and processes RF power by converting it into a proportional DC voltage. The detector rectifies and filters the RF signal to obtain an average DC voltage level proportional to the RF power.

CMOS power detectors offer several advantages, such as:

Low power consumption
Compact size
Compatibility with CMOS technology

CMOS Power Detector Functions

The functioning of a CMOS power detector can be broken into the following phases:

Rectification: A diode or a combination of diodes is used to rectify the RF signal. Diodes are biased, so they conduct during the positive half-cycle of an RF signal and block during the negative half-cycle. As a result of the rectification process, an AC RF signal is converted into a pulsating DC signal.
Filtering: The rectified pulsating DC signal is filtered to remove the high-frequency components and retain the average power information. A low-pass filter is typically used to smooth out the pulsations and maintain a relatively steady DC voltage.
Voltage Conversion: The filtered DC voltage is further conditioned to obtain a desired output voltage level proportional to the RF power. Depending on the application’s requirements, the DC voltage may be amplified, scaled, or attenuated.
Output Measurement: The CMOS power detector’s final output voltage can be measured using an analog-to-digital converter (ADC) or directly used for power control or monitoring within the RFIC.

CMOS power detectors are widely used in wireless communication systems, including cellular networks, WiFi, Bluetooth, and other RF-based applications, to accurately measure and control the power levels of transmitted and received signals.

CMOS Power Detector Design: Low Power vs. Wideband

Two common design variations of CMOS power detectors are low power and wideband.

Effects of Vortex Shedding on Marine Structures
Design Variation	Pros	Cons
Low Power	Low current consumption High power efficiency Designed for battery-powered devices Suitable for power-sensitive application	Limited dynamic range Reduced accuracy compared to wideband
Wideband	Higher dynamic range and better accuracy compared to low power Suitable for broadband communication systems	Consumes more power than low power Greater complexity

An application's specific requirements determine whether a low-power or wideband CMOS power detector is appropriate. Low-power detectors are more suitable if you want power efficiency and low current consumption. However, if accurate power measurements are needed across a wide frequency range, wideband power detectors are better even though they consume more energy.

Integrating a CMOS Power Detector Into a PCB

When integrating CMOS power detectors into PCBs, you should design the circuit layout, select appropriate components, and follow best practices for RF circuitry. In general, you can follow these ten steps:

10 Steps for Integrating a CMOS Power Detector Into a PCB
1) Circuit Design	Design your CMOS power detector circuit according to your application's requirements Select the appropriate CMOS power detector IC and determine its recommended application circuitry from the datasheet
2) Schematic Capture	Create a schematic diagram of the entire circuit, including: CMOS power detector Power supply connections Decoupling capacitors Input/output matching networks Additional filtering or amplification components
3) Component Selection	Select passive components, such as capacitors, resistors, and inductors, based on the datasheet of the CMOS power detector Ensure the chosen components meet performance, power, and impedance requirements
4) PCB Layout	Create the PCB layout using ECAD software Assemble the PCB, considering factors such as component placement for maintaining signal integrity, reducing parasitic effects, and optimizing RF trace lengths Pay attention to the power supply and ground routing to ensure low impedance paths and minimize noise
5) RF Trace Routing	Route the RF traces carefully, considering impedance control and transmission line techniques, and avoid excessive bends or sharp corners Maintain proper clearance between traces to minimize crosstalk and interference Follow the CMOS power detector's datasheet guidelines for RF trace routing and matching network design
6) Power and Ground Planes	Establish separate power and ground planes on the PCB Create a solid ground plane to provide a low-impedance return path for RF signals and minimize interference Stabilize the power supply and reduce noise by placing decoupling capacitors near the power supply pins of the CMOS power detector Add filtering components, such as inductors and capacitors, as required for noise reduction and harmonic suppression
7) Design for Manufacturability	Follow the design rules and guidelines provided by the PCB manufacturer to ensure that the PCB design is manufacturable Ensure the trace widths, clearances, and other design parameters comply with the fabrication process
8) Design Verification	Conduct thorough design verification, including electrical simulations and prototyping, to ensure CMOS power detector circuit functionality and performance Test the PCB for power detection accuracy, frequency response, and other relevant parameters
9) Documentation	Prepare accurate and comprehensive documentation, including: PCB layout Schematic Bill of materials Assembly instructions
10) Prototyping and Testing	Fabricate a prototype PCB and thoroughly test it to validate the performance of the CMOS power detector circuit Make any necessary adjustments or optimizations based on the test results

The details and considerations may vary depending on the CMOS power detector IC, application, and design requirements. Therefore, you should refer to the datasheet of the CMOS power detector IC and consult with PCB design experts for guidance throughout the integration process.

Signal/Power Integrity With CMOS Power Detectors

CMOS power detectors help ensure signal/power integrity for optimal performance, especially when it comes to wireless network strength. Cadence supports your work with SPICE simulations, constraint management for layout correctness/completeness, and other cutting-edge tools.

Leading electronics providers rely on Cadence products to optimize power, space, and energy needs for a wide variety of market applications. To learn more about our innovative solutions, talk to our team of experts or subscribe to our YouTube channel.

Request an Evaluation