ADS4149: SPI pin setting/ High Performance Mode

Shota,

HIGH PERF MODE1 improves aperture jitter of ADC by making input clock buffer stronger (by increasing its current by ~3 to 5 mA).

Impact on input frequencies: So you would see its impact mainly on high input signal frequencies where jitter noise dominates overall SNR of ADC.

For examples, you may see about 1 to 1.5dB improvement in SNR at -1dBFS with a 230MHz IF sampling at 250MSPS.

Impact on sampling frequencies: If the rise and fall time of clock signal is same across sampling frequencies, impact of this MODE should not depend on clock sampling rate. However, it has been seen, especially in case of sine wave clock, that the rise/fall time of clock signal degrades for lower sampling rates which in-turn degrades the aperture jitter of ADC’s clock buffer. Since this MODE makes the input clock buffer stronger, its impact is more visible at lower sampling rates.

In summary, the MODE is the most helpful for high IF/Low sampling clock combination, and its predominant impact is on SNR, may improve HD2 slightly (1dB or 2) as well.

Regards,

Jim