I want to measure RMS voltage of 5.8 GHz signal using AD5511.
what is the appropriate ADC to measure RMS voltage?
You mean ADL5511, correct?
The ADL5511 RMS detector block has provision for external square-domain averaging via a capacitor on pin 14, FLT4. Normally the external capacitor is chosen to smooth out the measurement and reduce the error effect that RF modulation would have contributed to the rms measurement. The larger the capacitor, the lower the ADC sample rate requirement. See datasheet Eq. (2) and Eq. (8), and Table 4. The ADC sample rate should be at least several times higher than fFLT4. ADC input range is recommended to include at least 0 to 3.8V, which is the output voltage range for VRMS, pin 11. ADC resolution is as required for the application, normally around 10 to 12 bits.
Thank you for the response.
I have selected ADC accordingly.
I have one more question.
For the input RF signal of frequency 5 GHz and amplitude 10.12 dBm, what will be the corresponding Vrms DC value at the output of ADL5511?
For the input RF signal of frequency 5 GHz and amplitude 10.14 dBm, what will be the corresponding Vrms DC value at the output of ADL5511?
Can ADL5511 differentiate between these two RF signals?
These two signals are generated from voltage controlled oscillator on PCB. NO SMA connector is involved.
See datasheet Figure 7. At Input= +10dBm, expect approximately 1 Volt at the Vrms output. We say 'approximately' because these devices are subject to production variation which is inherent to the semiconductor mass production process.
If input power increases by 0.02dB, Vrms DC output increases by about 2.3mV. It should be discernable with a good measurement arrangement.
See also datasheet Figure 38, showing how output will change with respect to the IC temperature. To accurately discern 0.02dB variation, you will need to keep temperature constant between the two measurements.
Thank you, sir, for the response.