We are using LTC5585 for generating quadrature signals. We have observed a gain of -20dB while in datasheet it is shown to have a gain of 2dB. Please clarify this issue.
Could you describe your test setup? If you are using a factory demo board, there should be DC blocks at each output, and then 180-degree power combiners for each I & Q output, as shown in the demo board manual.
Please note that the gain that we report in the datasheet is unloaded voltage conversion gain. This is because we don't know exactly how the user will terminate the demodulator output, and unloaded voltage conversion gain represents the highest voltage gain that the part is capable of.
If you're measuring power gain, there are some conversion factors to apply to calculate unloaded voltage conversion gain, as shown in datasheet.
Hi Bruce Hemp,
1. We have designed the PCB as recommended in the LTC5585 datasheet with same value of components shown. It is not the evaluation kit provided by Linear Technology.
2. We are using DC blocker at the output of LTC5585 output.
3. We are measuring the output at Spectrum analyzer. So there is no next stage that is causing the load.
Your spectrum analyzer has 50-ohm input impedance, so your are loading the output of the LTC5585 with 50 ohms. Therefore, your gain is reduced by
You did not mention whether you measured single-ended or differential output. The gain specified in the datahsheet is for differential.
I had measured single ended signal.
Retrieving data ...