RF Power Measurement System Using HMC948LP3E

Develop an RF power measurement system capable of accurately detecting and displaying RF signal strength over a specified frequency range.

1. HMC948LP3E: Logarithmic detector for RF signal measurement.
2. THS4511: Fully differential amplifier to interface the detector's output with an ADC.
3. ADS4222: Analog-to-Digital Converter (ADC) for digitizing the amplified signal.
4. Microcontroller (e.g., STM32 series): Processes the digitized signal and displays the RF power level.
5. Display Module (e.g., LCD or OLED): Visual representation of the measured RF power.

The system receives an RF signal within the operational frequency range of the HMC948LP3E.

The HMC948LP3E processes the RF signal, providing a DC output voltage proportional to the logarithm of the input signal's amplitude.

The output from the HMC948LP3E is fed into the THS4511 differential amplifier. Proper selection of feedback resistors (Rf and Rg) is crucial to achieve the desired gain and to match the input impedance requirements of the subsequent ADC stage. For instance, using 1kΩ resistors for Rf and Rg can be a starting point, but adjustments may be necessary based on specific design requirements.

The amplified signal is then digitized by the ADS4222 ADC. It's essential to ensure that the input signal to the ADC swings symmetrically around its common-mode voltage (e.g., 0.95V for ADS4222) to maintain signal integrity. This may require configuring a resistor divider network and utilizing the ADC's Vcm output as the reference for the amplifier.

The microcontroller reads the digitized data, computes the corresponding RF power level using calibration data, and formats it for display.

The calculated RF power level is presented on the display module in dBm or other relevant units.

Considerations:

1. Input Impedance Matching: Ensure that the input impedance of the amplifier is balanced to prevent differential output offset. For example, if the input source has low impedance, adjusting the resistor values (e.g., setting R256 to approximately 667Ω) can help balance the inputs.
2. Power Supply Configuration: The THS4511 can operate with a split supply (e.g., +3V and -2V) to accommodate the required signal swing and to interface correctly with the ADC's input range.
3. Calibration: Calibrate the system using known RF power levels to establish an accurate relationship between the detected voltage and the actual RF power.
4. Frequency Range: Verify that all components, especially the HMC948LP3E, operate effectively over the desired frequency range of the application.

By integrating the HMC948LP3E logarithmic detector with appropriate amplification, digitization, and processing stages, you can develop a reliable RF power measurement system suitable for various applications, including signal strength monitoring and spectrum analysis.