To Whom it May Concern,
Questions about AD9680 ADC converter:
1) Data sheet rev.B, Table 9 recommends ETC1-1-13 and BAL-00006SMG baluns.
The first one is 1:1 balun, the 2nd one 1:2 balun per respective data sheets.
Source impedance at balun's input is 50 Ohms.
Table 9 recommends the same termination resistors R1, R2 for both baluns despite the fact that baluns have different impedance ratios.
Is that correct?
2) ADC input R and C are configurable via SPI. Input configuration is on Figure 91, impedance options are on Figure 92.
I couldn't find in the data sheet what ADC input configuration is recommended for Figure 91.
What input R shall be selected?
What input capacitance shall be selected?
3) ETC1-1-13 is 1:1 balun. To have 50 Ohms input impedance it shall be loaded with 50 Ohms or very close to that.
If ADC input impedance is set to the highest 400 Ohms, then resistors network on Figure 91 will make balun load impedance of [25 * 2 + 2 * 25 parallel with 400] = 94.4 Ohms.
Balun's load impedance becomes 50 Ohms only if ADC inputs are shorted. But it doesn't seem to be a good idea...
94.4 Ohms is too low for BAL-0006DMG and is too high for ETC1-1-13.
So, I think Table 9 does not address the AD9680-1000 + ETC1-1-13 balun configuration.
What external network and ADC settings recommended for it?