> What if both inputs are terminated into a load (e.g. 50 ohms) rather than a short?
I tried to terminate the inputs with 50 ohm between the pin and the DC block cap (and even 1 Kohm). auto-oscillations are gone, but the loss of sensibility is catastrophic. From -30 dB at 2 GHz, it drops down to +5 dB. Tried with and without amp input stage. > When you say the eval board also oscillates, is that with the VCO removed from the circuit, or what? I removed C18, so VCO was disconnected. The "best practice" for this chip seems to decouple the RFINB input from ground with a 100 pF cap and use a DC block cap on RFINA directly to the pin. In that configuration, the ADF4107 oscillate. -----Message d'origine----- De : [email protected] [mailto:[email protected]] De la part de jimlux Envoyé : lundi 24 janvier 2011 02:02 À : [email protected] Objet : Re: [time-nuts] Update on prescaler board for HP 53131A-like counters On 1/23/11 4:27 PM, Samuel DEMEULEMEESTER wrote: > Hi timenuts, > > > > Here is an update for all of you interested by this project. According > to the emails I got, you are a lot ;-) > > What if both inputs are terminated into a load (e.g. 50 ohms) rather than a short? The input circuit in Fig 18 of the data sheet shows it going into a diffamp (which will be pretty Hi-Z differential) and tied through 500 ohms to the bias supply, which I assume would be (very) low Z to ground, so the input z is a few hundred ohms or so. Tying that straight to ground might not be the best way to put "no input" in. That is, the amplifier isn't stable with a mismatch on the input. Figure 27 shows a 51 ohm termination to ground (through a decoupling cap), fed by a resistive 2 way splitter. When you say the eval board also oscillates, is that with the VCO removed from the circuit, or what? > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
