Hi all,

I have a couple of simple questions regarding the spec of the AD8302 RF/IF gain and phase detector.

I know that in order to obtain a gain measurement, the maximum allowable difference between the 2 input signal amplitudes is 30dB (assuming you are working within the -60dBm to 0dBm range).

1. What is the output voltage VMAG if the difference between the 2 input signals is greater than +/-30dB?

What is not explicit in the datasheet is that if this the same for getting a phase measurement.

2. Another words, in order to obtain a phase measurement, What is the maximum allowable difference between the 2 input signal amplitudes? ie will I get a phase voltage if one input is 0dBm and the other one is -60dBm?

3. If I can get a phase voltage up to a difference of 60dB within the working range of of the 2 log amps (-60dBm to 0dBm), What kind of error will I get with the phase voltage VPHS?

4. When I look at the TPC curves say TPC 42 on page 12, it shows 3 curves and says

Phase Output voltage vs. Input Phase Difference, PINPA =PINPB, PINPA = PINPB + 15 dB, PINPA = PINPB – 15 dB, Frequency 900 MHz.

What is confusing me is that the 3 curves were pointed with an arrow indicating Pinpa=-15dBm, Pinpa=-30dBm, Pinpa=-45dBm.

So for example, which one of the 3 curves correspond to PINPA =PINPB? Can it be all 3? because you can have Pinpa=Pinpb=-15dBm, Pinpa=Pinpb=-30dBm, Pinpa=Pinpb=-45dBm. Or another example, which one of the 3 curves correspond to PINPA = PINPB + 15 dB? Again, can it be all 3? If so does that mean the curve for Pinpa=-15dBm = Pinpb (-30dBm) + 15dBm is identical to Pinpa=-30dBm = Pinpb (-45dBm) + 15dBm and also identical to Pinpa=-45dBm = Pinpb (-60dBm) + 15dBm? If so, does that mean the Phase Output voltage vs. Input Phase Difference is a function of the differences in amplitudes between the 2 inputs rather than the input levels (ie, Pinpa+Pinpb)?

5. If I am correct in that the Phase Output voltage vs. Input Phase Difference is a function of the differences in amplitudes between the 2 inputs, then what kind of errors will I get if one input is 0dBm and the other one is -60dBm?

Thank you so much.

Andy

Hi Andy,

Here the answers to your questions:

1. What is the output voltage VMAG if the difference between the 2 input signals is greater than +/-30dB?

What is not explicit in the datasheet is that if this the same for getting a phase measurement.

The outputs, both VMAG and VPHS are limited from a min of 0V to a max of 1.8V.

2. Another words, in order to obtain a phase measurement, What is the maximum allowable difference between the 2 input signal amplitudes? ie will I get a phase voltage if one input is 0dBm and the other one is -60dBm?

You will get an error in the VPHS slope and intercept if the input signal are not at the same amplitude. The greater the amplitude difference, the greater the error. See TPCs 42 through 47.

3. If I can get a phase voltage up to a difference of 60dB within the working range of of the 2 log amps (-60dBm to 0dBm), What kind of error will I get with the phase voltage VPHS?

You will get a voltage on VPHS, but it will probably be in error by a decent amount. We never tested a 60 dB difference in input amplitude. It will also be frequency dependent.

4. When I look at the TPC curves say TPC 42 on page 12, it shows 3 curves and says

Phase Output voltage vs. Input Phase Difference, PINPA =PINPB, PINPA = PINPB + 15 dB, PINPA = PINPB – 15 dB, Frequency 900 MHz.What is confusing me is that the 3 curves were pointed with an arrow indicating Pinpa=-15dBm, Pinpa=-30dBm, Pinpa=-45dBm.

No, the curves are not the same. Take a look at TPC43, this show the difference between the three curves presented in TPC42.

The error is mostly a function of the amplitude difference, not the amplitude level.

5. If I am correct in that the Phase Output voltage vs. Input Phase Difference is a function of the differences in amplitudes between the 2 inputs, then what kind of errors will I get if one input is 0dBm and the other one is -60dBm?

You will get the same errors shown in TPCs 42 through 47, only increased due to the greater disparity between the input amplitudes.

Hope this helps,

Joel