SHF Communication Technologies AG
Wilhelm-von-Siemens-Str. 23D • 12277 Berlin • GermanyPhone +49 30 772051-0 • Fax +49 30 7531078
E-Mail: sales@shf.de • Web: http://www.shf.deDatasheet
SHF 78120 B
Synthesized Clock Generator

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Description
The Synthesized Clock Generator SHF 78120 B is designed to provide our BERT customers with astandalone compact clock source featuring a wide frequency coverage from 0.625 to 38 GHz, high outputpower up to +8 dBm, low jitter and low harmonic levels. In combination with an SHF bit pattern generator
and error analyzer, it provides a compact and affordable high-speed test solution.
For frequencies above 10 GHz, additional band-pass filtering ensures low harmonic levels. Up to 10 GHz,
short rise time clock signals are generated in a trade-off for increased levels of higher-order harmonics.
The jitter injection functionality is integrated for jitter stress test applications. Arbitrary jitter types may be
applied to the clock signal using an external signal source, enabling various test scenarios such as data
protocol compliance testing. An optional internal jitter source provides sinusoidal jitter from 0.2 to 400 MHz
with variable jitter amplitude.
An additional trigger output provides a trigger signal whose frequency can be switched to a quarter orhalf the output frequency. The trigger remains jitter-free even if jitter injection is used.

Block DiagramFeatures

Output clock frequency ranges from fCLK = 0.625 to 38 GHz with 1 kHz resolutionOutput power adjustable from –10 to +8 dBm with 0.1 dB resolution

External and optional internal jitter modulation

Supports three spread-spectrum clocking (SSC) modes10 MHz reference input and output for phase locking to other instrumentsRemote programming interface (Ethernet, USB) for automated measurements

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Ease of Use
The SHF 78120 B is controlled over a standard Ethernet or USB connection by an external computer (notpart of the delivery). Every system comes along with the intuitive, easy to use BERT Control Center
software (BCC). The BCC provides the user friendly interface for changing the device parameters.
Additionally, the instrument may be programmed remotely over the Ethernet connection for automatedtests and measurements. Please refer to the SHF BERT Programming Manual.

Graphical User Interface

Options
Option ISJ: Internal Sinusoidal Jitter Source
Several data communication standards require jitter tolerance and jitter transfer testing for sinusoidal jitterover a specified jitter frequency range. The optional internal sinusoidal jitter source allows stress tests forjitter frequencies ranging from 0.2 to 400 MHz. Jitter amplitudes up to 60 ps may be generated. The jitter
amplitude is calibrated depending on the jitter frequency and on the clock frequency.

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Specifications
Parameter

Symbol

Unit

Min.

Typ.

Max.

CommentfCLK

GHz

0.625

Frequency Resolution

kHz1

Frequency Accuracy

ppb

–250

250

Using internalreference

Frequency Stability

ppb–50+50

Ambient
temperature 21°C

Frequency Stability Aging

ppb

–300

+300

per yeardBm–10+8Output Power Resolution

dB0.1

Output Power AccuracydB–1

Output Power Temperature
DriftdB/°C

0.1

Harmonics/Spurious Signals

dBc

–20

For fCLK ≥ 10 GHz

400

For fCLK ≥ 10 GHz;on scope display (not1deconvolved)

Clock Output (RF Out)Operating Frequency

Output Power Level

Pout

Phase Noise
Jitter (RMS)

dBc/Hz
JRMS

1fs
50

Connector
Parameter

Ambient
temperature 21°C

tbd

ΩOutput Impedance

38

2.92 mm (K) female
Symbol

Unit

Min.

Typ.

Max.

Frequency

GHz0.15625

19

Output Amplitude

mVpp

400

1000

Output ImpedanceΩCommentTrigger Out50Connector

2.92 mm (K) female

Option ISJ: Internal Sinusoidal Jitter Injection

1Jitter Frequency

MHz0.2400

Jitter Amplitude

ps060

Measured with Agilent 86100A, 70 GHz sampling head and precision time base triggered by Trig Out signal.

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External Jitter Injection
Modulation Frequency

MHz0.11000

Modulation Amplitude

mVpp

01200

Maximum corresponds
to 60 ps jitter.

Jitter Amplitude

ps060

Peak-to-peak

Input Impedance

Ω50Connector

2.92 mm (K) female

Spread Spectrum ClockingModulation Frequency

Hz10100 k

Deviation

ppm

020,000

Up/down/center

Ref InReference Frequency

frefMHz

Amplitude

Vpp

Input Impedance

Ω100.23.350Connector

SMA female

Ref Out (using internal reference setting)2

Reference Frequency

MHz10

Amplitude

Vpp

Output ImpedanceΩFrequency Accuracy

ppb

–250

250

Frequency Stability

ppb–50+50

Ambient
temperature 21°C

Frequency Stability Aging

ppb

–300

+300

per year

0.850

Connector

SMA female

GeneralPower Consumption

WWeightkg

Operating Temperature°C

25+12V switching power
supply is included

35Ambient temperature1102The specifications in this datasheet are only valid if the internal reference is activated. If the externalreference setting is activated the signal at Ref In is fed through to Ref Out. In this case the parameters
frequency, stability and amplitude depend on the Ref In signal.
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Typical Output Waveforms

BCC setting:
38 GHz, 0 dBm
Measurement results:
Vpp: 653 mV, Duty Cycle: 50 %BCC setting:
38 GHz, +6 dBmMeasurement results:
Vpp: 1258 mV, Duty Cycle: 50 %, Jitter (rms)*: 159 fs

BCC setting:
16 GHz, 0 dBm
Measurement results:
Vpp: 628 mV, Duty Cycle: 50 %BCC setting:
16 GHz, +6 dBm
Measurement results:
Vpp: 1219 mV, Duty Cycle: 50 %, Jitter (rms)*: 186 fs

BCC setting:
6 GHz, 0 dBm
Measurement results:
Vpp: 665 mV, Duty Cycle: 48 %BCC setting:
6 GHz, +6 dBm
Measurement results:
Vpp: 1290 mV, Duty Cycle: 48 %*Note 1: For improved accuracy, rms jitter measurements have been taken at a finer time resolution than the screenshot.
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Note that for clock frequencies above 10 GHz, the signal is band-pass filtered to achieve low harmonics
and a nearly pure sine wave. Below 10 GHz, however, the clock signals are amplified with subsequent
amplitude clipping to shorten the rise time. In the frequency range below 10 GHz, this generates
noticeable higher-order harmonics. The SHF 78120 B is optimized for clock source applications in
combination with SHF BERT instruments, where a short rise time is preferred.

Output Amplitude
The following diagram shows typical amplitude measurement results using a power meter connected
directly on the RF Out port for power settings from –10 to +8 dBm.

For clock frequencies above 10 GHz, the amplitude value in dBm, 𝑃𝑑𝐵𝑚 , can be converted from and to 𝑉𝑝𝑝using the following equations which are valid in a 50 Ω system:

𝑃𝑑𝐵𝑚 = 20 log10 (𝑉𝑝𝑝 ) + 4(Eq. 1)

𝑉𝑝𝑝 = 10(𝑃𝑑𝐵𝑚−4)/20.

(Eq. 2)

Note that below 10 GHz, the measured 𝑉𝑝𝑝 will be slightly smaller than the value calculated from (Eq. 2)
since the clock signals in that frequency range are square waves rather than single-tone sine waves.

External Jitter Injection
For additional flexibility, arbitrary jitter modulation may be applied to the high-speed clock signal. Jitter isinjected by connecting a signal source such as an arbitrary waveform generator to the external modulation
input. The maximum jitter amplitude is 60 ps peak-to-peak with a modulation bandwidth of up to 1 GHz. As
an example, the jitter amplitude of 60 ps corresponds to a relative jitter amplitude of 2.2 unit intervals (UI)
at a bit rate of 32 Gbit/s.
The jitter amplitude is calibrated using the Trigger Output signal of the SHF 78120 B which remains jitterfree even if jitter injection is used.
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In combination with an SHF Bit Pattern Generator and an Error Analyzer, the SHF 78120 B enables acomplete test solution for jitter tolerance tests as required by many telecommunication standards such as
100G Ethernet and 40 GBit/s OTN, FibreChannel, InfiniBand, PCI Express®, and Serial ATA. For furtherdetails please refer to the SHF application note „Jitter Injection using the Multi-Channel BPG“, available
online at www.shf.de.

Typical Jittered Signal Waveforms
The external modulation input can be driven by a function generator such as the Agilent 332XX family offunction / arbitrary waveform generators (AWG). The waveform characteristics of the AWG determine thejitter type of the SHF 78120 B.

Sine Wave on Modulation Input
SHF 78120 B

Sinusoidal jitter on 28 GHz clock.
AWG Setting
Waveform:
Frequency:
Amplitude:

Sine wave
100 kHz
70 mVpp

Gaussian-Distributed Noise on Modulation Input
SHF 78120 B

Random jitter on 28 GHz clock.
AWG Setting
Waveform:
Amplitude:

Noise70 mVpp

 InfiniBand is a registered trademark of the InfiniBand Trade Association. PCI Express is a registeredtrademark of Peripheral Component Interconnect Special Interest Group (PCI-SIG).
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Square Waveform on Modulation Input
SHF 78120 B

Peak-to-peak jitter on 28 GHz clock.
AWG Setting
Waveform:
Frequency:
Amplitude:

Square100 kHz
70 mVppSpread Spectrum Clocking
To meet the regulatory demands of electromagnetic interference several high-speed bus systems use aspread spectrum clocking (SSC) method. When SSC is enabled, the instantaneous frequency of the clock
signal varies periodically with time by a small amount, i.e. the clock signal is frequency-modulated. Thefigure below illustrates the SSC frequency modulation with a triangular shape.
InstantaneousFrequency

Frequency
DeviationTime
1/Modulation Frequency

The principle of SSC is the periodic frequency modulation of a clock signal.

The key SSC parameters are the following:
fCLK

original clock frequency without SSC

δrelative frequency deviation (often given in percent or ppm, parts per million)

fjittermodulation frequency.

The parameters are directly accessible in the BERT Control Center software GUI or through remote
programming.
Depending on the relative position of the clock frequency and the frequency deviation, SSC can beclassified into three types: down, center, and up-spread. The figure below illustrates the threeconfigurations.
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Down-Spread

Center-Spread

Up-Spread(1+δ) fCLK

Frequency(1+δ/2) fCLK
fCLK

fCLK

fCLK

(1–δ/2) fCLK

(1–δ) fCLK
1/fjitter

TimeTime

1/fjitter

1/fjitterTime

Three types of SSC.

SSC effectively broadens the spectral peak of a clock signal so that the maximum of the power spectral
density is reduced leading to less radiated emission. This is illustrated in the following spectra measured atthe output of the SHF 78120 B for a 25 GHz clock with 30 kHz modulation frequency and 0.5% deviation.
Note that SSC does not reduce the total signal power of the clock. Rather, it redistributes the clock’s spectral
components as shown in the figure below.

Without SSC

With SSC

Peak Reduction

SpectralBroadening

SHF 78120 B clock spectrum with and without SSC.

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Mechanical Drawing

All dimensions are specified in millimeters (mm).

Input/Output Connectors
Connector NameDescription

RF OutClock output

Trig Out

Trigger output

Modulation In

External jitter modulation input

Ref InExternal 10 MHz reference input

Ref Out

10 MHz reference output

Ethernet

Ethernet connectionUSB

USB socket

ServiceService connector – Do not connect

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