SBASAI7 March 2023 ADC34RF52
PRODUCTION DATA
The internal sampling clock path was designed for lowest residual phase noise contribution. The sampling clock circuitry requires a dedicated low noise power supply for best performance. The internal residual clock phase noise is also sensitive to clock amplitude and for best performance the clock amplitude should be larger than
1 VPP.
Frequency Offset (MHz) | Amplitude (dBc/Hz) |
---|---|
0.001 | -123 |
0.01 | -133 |
0.1 | -143 |
1 | -152 |
10 | -157 |
250 | -160 |
The clock input and ADC sampling circuitry also have an amplitude noise component which modulates on to the sampled input signal. Unlike phase noise, the amplitude noise does not scale with input frequency as shown in #FIG_FFX_L2S_NWB. This noise component can dominate the close in noise performance at lower input frequencies.
The internal aperture jitter is also dependent on the amplitude of the external clock input signal. #FIG_FQK_GTQ_BRBand #FIG_IRP_GTQ_BRB show the expected SNR performance with dither on/off across clock amplitude.
The sampling clock input is internally terminated to 100 Ω differentially and provides a return loss better than 10 dB (see #T5822397-1). The clock input consists of a single clock input buffer followed by a dedicated clock buffer for ADCA/B as well as ADCC/D. When averaging two ADCs internally, there is some decrease in clock buffer noise which is correlated and does not improve with averaging.