SiTime SiT6731EB User manual

SiT6731EB Manual Rev. 1.0
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SiT6731EB Evaluation Board
User Manual
Contents
1 Introduction ............................................................................................................................................. 1
2 I/O Descriptions ....................................................................................................................................... 2
3 EVB Usage Descriptions ........................................................................................................................... 2
3.1 EVB Configurations .......................................................................................................................... 2
3.2 Waveform Capturing Using Active Probe ........................................................................................ 3
3.3 Measuring Jitter and Phase Noise ................................................................................................... 3
3.4 Current Measurement ..................................................................................................................... 3
Appendix A.................................................................................................................................................... 4
1Introduction
The SiT6731EB evaluation board (EVB) is designed for use with SiTime’s Emerald OCXOs in the 10-pin
packages. It enables the evaluation of key functionalities of these OCXOs.
EVB Features
-SMA output for direct connection to measurement equipment
-Probing points for accurate waveform measurement
-Provision for future I2C control interface (connector)
-Connector for current measurement
SiTime typically ships the EVB with the OCXO mounted. The OCXO device should only be evaluated in its
original soldered down state for best signal integrity and frequency stability. For best results the device
should not be de-soldered and then re-soldered either manually or via reflow process.

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2I/O Descriptions
Table 1. SiT6731EB I/O
I/O
Description
Power
SMA connector (J1) or a two-pin connector (P4) for DC power supply.
VDD is connected to Pin 2, GND –to Pin1 of P4.
Pin 1 access
SMA connector (J3) provides access to the pin 1 of the OCXO in either OE mode or
VCTCXO mode (for future devices with VCTCXO support). In OE mode, pin 1 can be
left floating as there is an internal pull-up resistor.
Pin 2 access
A two-pin connector (P5) provides access to the pin 2 of the OCXO.
Frequency control
via I2C
A three-pin header (P1) provides access to I2C (SDA, SCL) for future I2C support.
Output
Oscillator output can be accessed either using active probe or SMA connector. The
test points for active probe are placed closely to the oscillator output for better
signal integrity (see Figure A2). The output pin of the oscillator can also be
connected to the SMA connector (J2) through the R9 source termination resistor.
Section 3.2 describes in details the recommended measurement configurations.
Current
Measurement
A two-pin connector (P3) enables measuring the current consumption of the device.
Service connectors
P2 is reserved for SiTime internal use only.
3EVB Usage Descriptions
3.1 EVB Configurations
SiT6731EB can be configured to support three OCXO configuration modes:
-OCXO with output enable (OE) is currently available
-VCOCXO with analog voltage control –provision for future support
-DCOCXO with I2C –provision for future support.
Figure A1 in Appendix A shows the complete electrical schematic of SiT6731EB. Components labeled
“DNP” are not assembled.
Oscillator output waveform can be measured with an active probe in all configurations. The value of the
load capacitor C3 can be adjusted to match the load conditions in the target application. This enables
the user to measure waveform characteristics under similar conditions as close to those on the target
board as possible.
Shipment Configuration
SiT6731EB is shipped without components labeled “DNP” on the schematic (see Figure A1 in Appendix A).

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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.

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Appendix A
Figure A1. SiT6731EB EVB Electrical schematics

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Table A1. Bill of Materials (BOM)
#
Reference
Designators
Description
Qty
SMD component size
Value
1
C1
Capacitor
1
Case A
10uF
2
C2
Capacitor
1
0603
0.1uF
3
C3, C4
Capacitors
2
0603
DNP
4
D1
LED
1
0603
Green
5
J1
SMA connector
1
-
DNP
6
J2, J3
SMA connector
2
-
-
7
P1
3-pin header
1
-
-
8
P2
5-pin header
1
-
-
9
P3, P4
2-pin connector
2
-
-
10
P5
2-pin header
1
-
-
11
R1, R2, R5, R6,
R10, R11, R12
Resistors
7
0603
DNP
12
R3, R4, R8, R9
Resistors
4
0603
0 Ω
13
R7
Resistor
1
0603
160 Ω
Table A2. Connectors Digi-Key Part Number
Connectors
Digi-Key
part number
Digi-Key
part number for
mating connector
Digi-Key
part number for
associated products
Power
WM2744-ND
WM5534-ND
WM2011-ND
WM1114-ND
Pin 1 access
WM5534-ND
-
-
Pin 2 access
732-5315-ND
Frequency control via I2C
732-5316-ND
-
-
OUT
WM5534-ND
-
-
Current Measurement
WM2744-ND
WM2011-ND
WM1114-ND

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Figure A2. SiT6731EB EVB
Signal
Probe test
points
GND
VDD

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SiT6731EB Evaluation Board User Manual
Table 2: Revision History
Version
Release Date
Change Summary
1.0
12/13/2018
Original doc
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