ADRF6520's input common mode voltage is 1.375V, while output common mode is 1.65V. There is no on-chip mechanism to change these common-mode voltages, so you must match the pre- and proceeding stages to the ADRF6520's common-mode.
The LTC5594's IF Amps' output common-mode voltage is 0.9V by default, but can be change from 0.5V to 2.0V via the Vcm pin. I'd drive Vcm = 1.375V to match that of the ADRF6520.
You might have to implement a level shifter between the output of the ADRF6520 and the input of the AD9684, to shift from the 1.65V to 2.05V on the AD9684's input.
Is DC coupling a must for your application? With the larger signal BW's in the Receive chain, it is often unnecessary to DC couple given one uses large enough AC coupling caps.
Thank you for your help but I already know everything written in datasheets. I need an implemented demonstration applicable for Zero IF. As written on the top of my image shared, it is a Zero-IF application, so DC coupling is a must.
Please send me a level shifter for that apllication specific case.
Understood that application is Zero-IF. However, for all but the smallest of signal bandwidths, having a small amount of the signal corrupted by a high-pass corner, that is low enough in frequency, will have little to no effect on the EVM/BER. I have done this measurement on the bench and would recommend trying this out before pursuing a DC coupling/Level Shifting scheme. AC coupling could be a much more simple solution.
Perhaps there are other aspects of your application that I am not considering that need AC coupling?
I decided to use AC-coupling. Can you please send me a reference interface connection for above diagram. I need AC- coupled connection from LTC5594 to ADRF6520 and from ADRF6520 to AD9684.
İn data sheet og AD9684 there is no information about direct differential connection from demodulator output to ADC input. There are some information just for transformer coubling.
In addition to setting LTC5594's Vcm pin to 1.375V, you also need to properly set the output ground return resistors, R3-R8. The LTC5594 has current-mode IF outputs that require a termination resistance to create output common-mode voltage. The optimum current is around 18mA per output pin. The internal feedback adjusts the current to match the output common-mode voltage to what is set on Vcm.
Thank but what must be the R3-R8 resistors value for 1.375V ?
Can you have a look at the below VCMs which are feeded from ADR4520 voltage ref IC? Is The curent supplied from ADR4520 enough or NOT? AND What are you suggestions If I use those components as design below? Does it work or NOT?
I you do not mind, I will say a few words for shsiao, who is out of office for a while.
LTC5594 has internal DVGAs, plus internal output amplifiers designed to directly drive most common high-speed ADCs. For most applications, another driver IC is unnecessary. LTC5594 output Vcm range is specified as 0.5 to 2.0 V. Best performance is at Vcm= 0.5 to 0.9V, as shown in datasheet Figure 12. AD9684 requires Vcm= 2.05V +/- 100mV. The LTC5594 can do this, but there will be some degradation of OIP3 performance as shown in Figure 12.
In general, the Vcm imputs are measured in kOhms, so adequate current drive capability is usually not a problem.
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