Clock Signal Probing Options
The following table describes the clock source probing options for phase noise analysis. Note that two copies of a signal are required in order to use the two-channel cross-correlation technique to lower the oscilloscope's noise floor.
| Clock signal type | Connection method (into #input channels) | Phase noise source 1 (for example) | Phase noise source 2 (for example) | Uses 2-channel cross-correlation technique | Notes |
|---|---|---|---|---|---|
|
Single-ended |
Direct (1) |
Channel 1 |
None |
No |
|
|
Single-ended* |
Split (2) |
Channel 1 |
Channel 2 |
Yes |
See Single-Ended Signals. |
|
Differential |
Converted into a single-ended difference signal using a balun transformer or limiting amp (1) |
Channel 1 |
None |
No |
|
|
Differential |
Converted into a single-ended difference signal using a balun transformer or limiting amp, then split (2) |
Channel 1 |
Channel 2 |
Yes |
|
|
Differential |
DiffP, DiffN (2) |
Channel 1 |
Channel 2, inverted |
Yes |
Does not yield the correct result if there is common-mode noise on the differential clock or if there is uncorrelated noise on one of the polarities of the differential signal. |
|
Differential |
Single-probed using one differential probe (1) |
Channel 1 |
None |
No |
Not recommended because a probe's attenuation of the SUT reduces signal-to-noise ratio (SNR). |
|
Differential |
Double-probed using two differential probes (2) |
Channel 1 |
Channel 2 |
Yes |
Two-channel cross-correlation removes probe and input channel noise. However, double-probing is more difficult to attach and gives twice the loading. See Probes. |
|
Differential* |
DiffP split, DiffN split (4, for example, DiffP1 into ch1, DiffN1 into ch3, DiffP2 into ch2, DiffN2 into ch4) |
Channel 1 - 3 |
Channel 2 - 4 |
Yes |
Best signal-to-noise ratio. See Differential Signals. |
| * = recommended for this signal type | |||||