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?

Thank you,

Mike

Hi Mike

Thank you for contacting Engineer Zone regarding the AD9680.

1. Yes. This is correct. The ADC evaluation board yielded same results for both ETC1-1-13 and BAL-0006 baluns.

2. Please see Table 10 for the input R/C settings

3. Not sure if 94.4Ohm is too low for the BAL-0006SMG. the data you see in the datasheet is taken using the configuration shown in figure 91 with the default ADC termination R and C.For the ETC1-1-13, we have tried (reference figure 91) R1/R2 = 10/50 and R1/R2 = 10/25. Both gave acceptable performance (regardless of match) at low frequencies and higher than normal second harmonic degradation at >500MHz.

You can try these setups on your end by purchasing the AD9680-LF1000EBZ

Thanks

Umesh