What is the RFinA and RFinB impedance over frequency?
The combined impedance of the input biasing and input differential stage is targeted at 50ohmns, we don't have S parameters for the ADF4002 , however the ADF411X family datasheet has S parameters that will be close to what we would expect for the ADF4002, see the following page:
I moved this question about the ADF4002 to the RF Components Community. Someone here should be able to assist you.
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I have one more question about the ADF4002. What is the phase noise floor of the MUXOUT pin on the ADF4002? I have an application where I'd like to use the 4002 as a standalone low noise programable divider using the RFin a/b inputs and the muxout pin.
I have a, ADF4002 Eval board set up with an SMA connection from MUXOUT, first I did a phase noise measurement on the 200Mhz signal generator at 10Khz, 100Khz and 1Mhz offsets, results were -146dBc/Hz, -148 dBc/Hz and -157 dBc/Hz respectively, when I connected this source to RFOUT on the eval board and programmed N =1, the PN measurement at MUXOUT at 200Mhz for the same frequency offsets were -135dBc/Hz, -138dBc/Hz and -140 dBc/Hz
I hope tihs helps, regards.
Were you able to take this data?
I sent you the following in the previous mail...
" ADF4002 Eval board set up with an SMA connection from MUXOUT, first I did a phase noise measurement on the 200Mhz signal generator at 10Khz, 100Khz and 1Mhz offsets, results were -146dBc/Hz, -148 dBc/Hz and -157 dBc/Hz respectively, when I connected this source to RFOUT on the eval board and programmed N =1, the PN measurement at MUXOUT at 200Mhz for the same frequency offsets were -135dBc/Hz, -138dBc/Hz and -140 dBc/Hz "
does this help with your question on phase noise at MUXOUT ?
I will take a measurement further out at the noise floor and will get back to you shortly. Regards,
I took a PN measurement at 10Mhz, 20Mhz and 30Mhz, and all were at -140dBc, so we are measureing -140dBc phase noise floor at MUXOUT for a divide by 1 RFIN signal , Regards,
I never received the previous email. Yes, that is very helpful. Thank you!
"The combined impedance of the input biasing and input differential stage is targeted at 50ohmns, we don't have S-parameters for the ADF4002 , however the ADF411X family datasheet has S parameters that will be close to what we would expect for the ADF4002..."
The above seems to imply that the RFin impedance of the ADF4002 is in the neighborhood of 50 ohms. However, using the S-parameters provided in the ADF411x family datasheet that you referenced, at 200MHz the RFin impedance appears to be 1339 - 1334j. At 50MHz, the input impedance is 798 - 250j based upon the S-Parameters that are provided. I am using a Mini-Circuits JTOS series VCO with an output that varies from about 7dBm to 10dBm. In order to match the output of the JTOS-50 with the ADF4002 input range of 0 to -10dBm, I plan to use a resistive attenuator and for that I need to know the input impedance of the ADF4002. The only way I can reconcile the S-parameters with the statement regarding 50 ohms is to assume that the S-parameters were taken at low power with the diodes staying off, and that at higher power, the diodes turn on, effectively reducing the input impedance. What is the best way to model the input of the ADF4002 so that I can properly attenuate the VCO output for ADF4002 input?
Hello Mr Matthews,
We have modeled the RFin for the ADF4002 in our evaluation board as 50ohmns... we can recommend that your attenuator presents a 50ohmn source ac coupled to RFIN.
See UG108 as a reference...note: the input differential diodes RFIN+/RFIN- and input ESD diodes turn on in the event of an overvoltage condition, operation is not specified with these diodes conducting.
I have read the datasheet for the UG-108 and ADF4002.
Figure 21 of the ADF4002 datasheet shows a single ended output from an external prescaler matched to the RF input A of the ADF4002 using a 100pF series capacitor and a 51 ohm shunt resistor.
The datasheets for the AD500x family of external prescalers specify a 50 ohm load for single ended operation.
If the ADF4002 has an input impedance of 50 ohms, then the load seen by the external prescaler shown in Fig. 21 ranges from about 35 ohms to 25 ohms over the frequency range of 25MHz to 400MHz. This is a very poor match.
If it is assumed that the combination of the 51 ohm shunt resistor and the 100pF series capacitor provides an excellent 50 ohm match to the prescaler in Fig. 21, then the input impedance of the ADF4002 would have to be about 2500 ohms.
If, as you maintain, the input impedance of the ADF4002 is 50 ohms, then why is a 51 ohm shunt resistor being used to match the external prescaler in Fig. 21?
I will confirm the input impedance of the ADF4002 between 25MHz to 400Mhz, and will post it here.
note: Figure 21 may not have been designed for optimum matching.
Retrieving data ...