SiT6731EB Manual Rev. 1.0
SiT6731EB Evaluation Board User Manual
3.2 Waveform Capturing Using Active Probe
SiTime OCXO is a high speed logic output device. It is critical that the proper logic and high frequency
measurement techniques are used along with the high quality active probe in order to ensure best
measurement results.
SiTime recommends the following minimum equipment for proper clock waveform measurement
1) GHz or higher active probe with capacitance <1 pF, such as an Agilent1134A;
2) Oscilloscope with 4GHz bandwidth or higher such as a DSA90604A.
A passive voltage probe should not be used as it adds a high capacitive load to the part and the long
ground lead clip is not suitable for high frequency measurement applications. The inductance of the long
ground lead coupled with the input capacitance of the probe results in a resonant circuit. The
consequence of this resonance results in the distortion of the clock signal. Typical manifestations of this
distortion include ringing, overshoot, and undershoot of the clock signal.
Eliminating such distortion requires a probe with the lowest input capacitance and a low inductance
ground lead. In addition, SiTime OCXOs are typically configured for fast rise and fall times (1 ns or less)
with 15 pF load. It is therefore critical that the probe tip ground be as short as possible, lowest
inductance, and the return path for the ground be located as close as possible to the trace carrying the
RF logic signal. Please refer to Figure A2 for test point locations on the SiT6731EB and an example of
proper probing.
3.3 Measuring Jitter and Phase Noise
For jitter measurements, make sure that SMA connector and source termination resistor R9 are properly
soldered on the EVB. The R9 can be populated using one of the following options:
1) 0Ωresistor. This allows DC coupling the output to 50Ωinstruments directly. Note that due to
50Ωloading, the signal swing levels and rise/fall times will be different from those specified
in the datasheet.
2) 0.1uF capacitor for AC-coupling to 50Ωinstruments.
SMA connector is used to connect directly to the jitter measurement instrument, such as Time Interval
Analyzer (TIA) or high-bandwidth real-time oscilloscope. Jitter measurement technique is described in
SiTime AN10007.
The SMA can also be connected through 50Ω coaxial cable to signal source analyzers or spectrum
analyzers to measure phase noise. In such case the use of AC-coupling configuration is recommended
because not all measurement instruments can accept DC voltage at their inputs.
3.4 Current Measurement
To measure the current, remove zero-ohm resistors R3, R4, and connect the DMM or other current
measuring device across P3 connector. It is recommended to measure the voltage on DUT VDD and
adjust for any drop on the DMM to ensure known VDD voltage on the device. VDD adjustment has to
be completed before every current measurement.
