Dear Supporter,

I am using AD9864 in our project. Now I faced a problem about RSSI.

Could you please help clarify the relationship between the RSSI values and real power? or give some comments on my issue?

thanks so much for your kindly help and support!

Br,

Wayne

Hello,

The RSSI is a coarse "linear detector" that measure the ABS(I)+ABS(Q) value of the input signal has shown in figure 58. It is typically used in conjunction with the AGC since its output is compared to the programmable level set in the AGCR field. The RSSI is a 6-bit field (when enabled) in the SSI output data with a value of 60 corresponding to a 0 dBFS sinewave input at IF center ( and -6 dBFS corresponding to a a value of 30).

If the VGA setting is known than it is possible to calculate the real power from the IQ output (within digital passband with higher accuracy) or the RSSI field (wider band with lower accuracy due to 6-bit linear resolution). For examplle, if its setting was set to 0 dB (i.e. ONLY VGA Enabled in figure 59) than a -32 dBm input signal will result in a -2 dBFS level (defined as IF "clip point") on the I/Q output ...........hence 0 dBFS = -30 dBm is my reference point.

If the signal generator was reduced by 4 dB to -36 dBm................I would expect the RSSI field to read closer to 30 since this corresponds to -6 dBFS).

Note that the freqency offset from the IF center also introduces an additonal error as shown in figure 60.

Again..............the RSSI function is typically used in conjunction with the AGC and only provides a coarse estimate of the signal power over the extended freq range of the 1st stage Dec-12 filter.