Analog Band Pass Tunable Filters (ADMV8420,ADMV8416,HMC892A,HMC891A)

Hi Aram,

Sorry for the late reply. You are on the correct thinking regarding speed and noise performance.

In the past we have used the AD5760 DAC followed by the ADA4898 op-amp as a unity gain buffer. The DAC reference was the LT3042 voltage regulator set to 15V. This resulted in excellent baseband noise spectral density on the order of 10nV/rtHz, so the residual phase noise floor of the filter would not be impacted (better than -150dBc/Hz). The downside was the voltage tuning speed was on the order of 1usec, which isn't quite your desired 200nsec time.

You might find a faster DAC or op-amp in the catalog, but keep in mind the baseband noise spectral density may impact phase noise results. As a rough order of magnitude for phase noise floor, you could use small angle phase modulation equation of 20*log(Vnoise_in_rms * Filter_Phase_Sensitivity / sqrt(2)).

Best Regards,

David

HI, The AD5760 voltage is only ±10V. While the HMC voltage control is from 0 to 14V. Did you use the OP amp to adjust the voltage output?

Hi Andri,

For the AD5760 DAC you can use a wider voltage range than the nominal +/- 10V on the voltage reference. Have a look at the datasheet +/- 16.5V is possible for VSS and VDD. The reference voltages are required to be narrower by 2.5V, so VREFN = VSS + 2.5V, and VREFP = VDD - 2.5V.

Previously we used the VSS=-5V, VDD=+17.5V, VREFN=0V, and VREFP=15V. Selection of these voltages was due to sharing supply with unity gain ADA4898 OPA, that had a typical dropout of 2.5V from the rails.

The ADA4898 OPA is only used as a buffer, so if tuning speed isn't a requirement than you can drive the filter tune voltage directly from the DAC. In that case, the DAC voltages could be VSS=-2.5V, VDD=16.5V, VREFN=0V, and VREFP=14V.

Best Regards,

David

Thank you very much for reply.

Appreciated. 

I'm using ADA4898 with AD9708ARUZ to achieve max. tuning speed. Also I have added in OPA feedback in-the-loop correction schematic as show below, for front glitch's compensation .

Best Regards

Aram Khachatryan

Hi, Thats a nice result. Could you inform me what OPamp feedback you use here?

Thanks

Hi, Thats a nice result. Could you inform me what OPamp feedback you use here?

Thanks