VCB response time

Question

Hi, 
 The HMC8362 has a pin which controls the buffer supply voltage: Vcb pin #8, 
 what is the response time VS RF? 
 I mean: can I control RF ON/OFF by modulating the buffer supply voltage with duty cycle 5 us ON - 5us OFF? 
 Many thanks 
 Andrea

enash · Accepted Answer

I've been unable to find any data on the response time of the VCB pin. I did however find some indirect information that may be useful. We tested the turn on time of the VCOs by pulsing on the VCX pins and found that they were turning on in around 10ns. That suggests that the turn on response of VCB will be equally fast because it's pulling less current. You do need to make sure that the source that is driving VCB can quickly deliver the 9mA required to turn on the output buffer. Looking at the evaluation board schematic, I see that there is already an inline switch (ADG854) on the board which you could use to test the response time (ADG854 switching time is 17ns). However there is another caveat. On the evaluation board circuit, I also see a lot of decoupling and ferrite beads in the VCB supply line. These will slow down the rise time. You can remove them but you would need to check that the phase noise at the output is not degraded. I think that your best bet is to get the evaluation board. This will allow you to test the response time using the switch and also start stripping away caps and ferrite beads (if needed) while verifying that you are still getting the desired phase noise.)

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VCB response time