UXG Multi-Box Synchronizationrfmw.em.keysight.com/wireless/helpfiles/n5193a... · UXG Multi-Box Synchronization Keysight Technologies, 2015 Page 4 Definitions System Controller A

UXG Multi-Box Synchronization Draft (Rev 5.1) 6/15/2015 Keysight Technologies Rick Richard

UXG Multi-Box Synchronization

Keysight Technologies, 2015 Page 1

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Table of Contents Table of Figures ............................................................................................................................................. 3

Definitions ..................................................................................................................................................... 4

Overview ....................................................................................................................................................... 5

Standard Four-Box Setup .............................................................................................................................. 5

Triggering .................................................................................................................................................. 6

Cabling....................................................................................................................................................... 6

Master UXG Trigger Assignments ......................................................................................................... 7

Slave UXG Trigger Assignments ............................................................................................................ 8

Master-To-Slave Trigger Routing .......................................................................................................... 9

6GHz Reference Routing ..................................................................................................................... 10

Sync Cable Routing .............................................................................................................................. 11

Synchronizing .......................................................................................................................................... 12

Cabling ................................................................................................................................................. 12

Role Selection ...................................................................................................................................... 12

Front Panel Synchronization Process .................................................................................................. 13

SCPI Synchronization Process ............................................................................................................. 14

Phase Accumulator Time Offset Adjustment .............................................................................................. 15

Master System Trigger Source Selection (A.01.15+)................................................................................... 16

Expanding Beyond Four Boxes .................................................................................................................... 17

6GHz Clock .............................................................................................................................................. 17

Sync Signal ............................................................................................................................................... 17

Trigger Fan-Out ....................................................................................................................................... 17

Daisy-Chaining Trigger Fan-out (A.01.20+) ......................................................................................... 18

Using Active Splitters for Trigger Fan-out ........................................................................................... 19

Input Trigger Metastability Issues (8ns trigger uncertainty) ...................................................................... 20

Using a System Controller In Place of a Master .......................................................................................... 21



Table of Figures Figure 1: Master UXG Trigger Assignments .................................................................................................. 7

Figure 2: Slave UXG Trigger Assignments ..................................................................................................... 8

Figure 3: Master Trigger Fan-out .................................................................................................................. 9

Figure 4: 6GHz Connectors and Jumper (Remove) .................................................................................... 10

Figure 5: 6GHz Clock Routing ..................................................................................................................... 10

Figure 6: Sync Cable Routing Diagram ....................................................................................................... 11

Figure 7: Multi-Box Role Selection (Front Panel) ....................................................................................... 12

Figure 8: Front Panel Synchronization Process .......................................................................................... 13

Figure 9: Coherent Phase Accumulator Time Offset Adjustment (front-panel) ........................................ 15

Figure 10: Multi-Box Sync Master System Trigger Selection ..................................................................... 16

Figure 11: Connector Routing For Multi-Box Sync Trigger Fan-Out (A.01.15+) ......................................... 17

Figure 12: Multi-box Synchronization Trigger Fan-out Daisy-chaining ....................................................... 18

Figure 13: Externally Buffered Trigger Fan-Out ......................................................................................... 19

Figure 14: Persistent Trigger Trim Delays ................................................................................................... 20

Figure 15: Possible "Masterless" Configuration ......................................................................................... 21



Definitions System Controller

A customer or vendor-supplied controller that directs a multi-box system. The system controller may be

conceived as a high level orchestrator of the UXG multi-box system and other hardware. It may be

responsible, for example, for providing the master system reference clock, trigger clock, trigger pulse, or

a sequence of SCPI commands.

Master

The UXG in a multi-box system designated as a master. The master UXG emits a training signal on the RF

SYNC OUT connector used for synchronization; may provide the master 6GHz reference clock; and

buffers, synchronizes, and retransmits a single trigger source to all UXGs in the system. The master

receives a synchronous clock on the Trigger1 connector.

Slave

One or more UXGs in a multi-box system designated as a slave. A slave UXG receives a training signal on

the 1-250MHz IN connector used for synchronization. It receives a 6GHz reference clock common to all

instruments on the 6GHz IN connector. A slave also receives a synchronous clock on the Trigger1

connector.

Master System Trigger

This is a single trigger source that will be buffered and fanned-out to all instruments in the system. This

trigger could be generated by the master UXG or by an external system controller.



Overview Electronic warfare receivers must sort millions of pulses per second from hundreds to thousands of

different radars and other emitters at a distance of up to 1000 kilometers between frequencies of 0 to

40 GHz. Each incoming RF pulse is parameterized into a digital pulse descriptor word (PDW) containing

the frequency, time-of-arrival, angle-of-arrival, pulse width, and modulation-on-pulse (AM, FM, PM),

and, to a lesser extent, the analog characteristics of the pulse such as rise time and overshoot. These

PDWs are sent to an algorithm that primarily sorts them based on frequency and angle-of-arrival of the

pulse since these parameters change the slowest. Depending on the range of the emitter, the angle-of-

arrival of a radar pulse might change over several seconds for an aircraft flying near the speed of sound.

Angle-of-arrival (AoA) is measured in three main ways,

amplitude comparison monopulse: the arctangent of the magnitude of the same RF pulse

measured simultaneously in two different receive channels

phase interferometry: the phase difference of the same RF pulse measured in different receive

channels separated by a known distance

time difference of arrival (TDOA): the time difference of the same RF pulse measured in

different receive channels separated by a known distance.

Of these, amplitude-comparison is by far the most common, especially in legacy systems. Amplitude-

comparison monpulse direction-finding gives AoA accuracies of 5-10 degrees RMS. New systems

increasingly rely on interferometry and TDOA with give AoA accuracies of less than 1 degree RMS. Some

receivers may use different methods in different sub-receivers in fields-of-view.

To test these receivers, AoA must be simulated in a multi-emitter environment. Agile sources, such as

the UXG, must be synchronized in phase and time so that phase, amplitude and timing offsets can be

created between otherwise-identical RF pulses injected into different receive channels on the system-

under-test (SUT). After synchronization, a calibration must be performed to know and then correct the

initial phase, time, and amplitude offsets between source channels before modifying the offsets to

simulate AoA.

Multi-box synchronization is designed to make a system of UXGs have a repeatable timing relationship

to one another with regards to their DDS phase accumulators and triggers. These time offsets can then

be corrected for in order to guarantee predictable and repeatable phase that will survive instrument

power-cycles.

Standard Four-Box Setup The first release of UXG firmware is able to support up to four UXG’s in a multi-box system without any

additional third-party hardware. Greater than four-box systems are not yet supported but are planned

for in the future. Additional hardware and firmware enhancements may be required.



Triggering There are several important considerations regarding consistent triggering in a multi-box system:

UXG trigger inputs are synchronous and are captured at a rate configured by the trigger clock.

Various internal and external path delays result in inconsistent arrival time at the hardware.

External factors such as cable length cannot be known.

If a synchronous trigger pulse is narrower than or equal to the trigger clock, it must be aligned to

the rising edge of the trigger clock to be reliably registered.

Asynchronous triggers must have a pulse width larger than the trigger clock pulse width.

UXG multi-box sync employs the following strategy to deal with the above issues:

Trigger1 on all instruments has a hardware delay element that is used to align a synchronous

trigger for reliable capture and to eliminate metastability.

An external master system trigger is to be received on the master UGX trigger 2 connector. It is

then brought into the system clock domain and retransmitted synchronously on triggers 3-6.

Trigger cable lengths should be electrically length matched as closely as possible.

The following trigger sources are available on the master for use as the master system trigger source:

EXT Trigger2

Timer Trigger (A.01.15+)

Trigger Key (A.01.15+)

BUS/*TRG (A.01.15+)

Cabling In a standard four-box configuration, one UXG is designated as a master and up to three slave UXGs can

be added to the system. The master generates a sync signal on the RF SYNC OUT connector and fans

out a synchronous trigger to all UXG’s in the system.



In this configuration, some trigger connectors have specially defined functions:

Master UXG Trigger Assignments

Trigger1 receives the synchronized system trigger.

Trigger2 is the external master system trigger connector.

Trigger3, Trigger4, Trigger5, and Trigger6 buffer and retransmit the synchronized master

system trigger.

Figure 1: Master UXG Trigger Assignments



Slave UXG Trigger Assignments

Trigger 1 receives the synchronized system trigger

Figure 2: Slave UXG Trigger Assignments



Master-To-Slave Trigger Routing

Figure 3: Master Trigger Fan-out



6GHz Reference Routing

The 6GHz jumper must be removed and the 6GHz OUT connector of the master UXG should be passively

split and routed to the 6GHz IN connector on all UXGs in the system:

Figure 4: 6GHz Connectors and Jumper (Remove)

Figure 5: 6GHz Clock Routing



Sync Cable Routing

The sync cable is daisy-chained from one UXG’s RF SYNC OUT connector to the next UXG’s 1-250MHz IN

connector, starting with the master.

Figure 6: Sync Cable Routing Diagram



Synchronizing In order to bring the system of UXGs into a consistent state, first they must be cabled as previously

described and their multi-box synchronizations roles must be properly selected (one master and up to

three slaves), then a synchronization procedure is completed either by the front panel or remotely via

SCPI.

Cabling

See previous section on cabling.

Role Selection

Note: Multi-box Sync State must be OFF in order to change the role of a UXG. It is not permitted to

change roles while Multi-box sync is currently active.

SCPI Role Selection

[:SOURce]:MBSync:ROLE MASTer|SLAVe

Front Panel Role Selection

Figure 7: Multi-Box Role Selection (Front Panel)



Front Panel Synchronization Process

Press “Begin Master Sync” soft key on master. o The master status window states “Press "Begin Slave Sync" on all slaves before

proceeding.” o Must sync to itself first before slaves, and then output a sync signal (output signal

may be ignored if customer supplies sync signal)

Press "Begin Slave Sync" on all slaves. o Each slave status window states “After pressing “Begin Slave Sync” on all slaves,

press “Prepare for Phase Reset” on the master, and then press “Await Phase Reset”.”

Press “Prepare for Phase Reset” on the master. o The master status window states “Press “Await Phase Reset” on all slaves so that

each shows a busy bar, then press “Initiate Phase Reset””.

Press “Await Phase Reset” on all slaves. o A busy bar will pop up on the screen.

Press “Initiate Phase Reset” on the master.

All units should announce “Synchronization Process Complete.” Note: The “Abort Synchronization” soft key will cancel the process at any stage.

Note: The trigger delays will need to be updated if the cabling has been changed since the last

synchronization, or this is the first time.

Figure 8: Front Panel Synchronization Process

Begin Master Sync

Master Box soft key

Begin Slave Sync

Slave Box(es) soft key

Press "Begin Slave Sync" on all slaves, then press “Prepare For Phase Reset”.

Await Phase Reset Prepare For Phase Reset

Press “Await Phase Reset” on all slaves so that each shows a busy bar,

then press “Initiate Phase Reset”

Initiate Phase Reset

All instruments should announce “Synchronization Process Complete.”

Status Message

After pressing “Begin Slave Sync” on all slaves, press “Prepare for Phase Reset” on the master,

and then press “Await Phase Reset”.

Busy Bar pops up



SCPI Synchronization Process

The following procedure can be performed remotely by SCPI to complete the synchronization process:

On master: “[:SOURce]:MBSync:MASTer:SYNChronize STAGe1”

On master: “*OPC?”

On all slaves: “[:SOURce]:MBSynchronize:SLAVe:SYNChronize STAGe1”

On all slaves: “*OPC?”



On all slaves: “[:SOURce]:MBSync:SLAVe:SYNChronize STAGe2”

On all slaves: “*OPC?”



Process complete. At this point, the “[:SOURce]:MBSync:MASTer:SYNChronize?” and “[:SOURce]:MBSync:SLAVe:SYNChronize?” queries will return “NONE”. If the STAGes are entered out of order, the process will fail, an error will be reported, and the stage will be set to “NONE”. If the master or slave SCPI commands are used on the wrong kind of instrument, then an error will be reported and the command is ignored.



Phase Accumulator Time Offset Adjustment The coherent phase accumulator of each UXG in a multi-box system is reset as part of the

synchronization process. Although this brings each UXG’s phase accumulator into a repeatable state,

there will exist a small time offset from one UXG relative to another due to variation in the propagation

delay of the trigger pulse that initiates the reset. The main contributor to this offset is the electrical

length of the trigger and sync cables used in the system.

A means is provided to directly manipulate the UXG coherent phase accumulator in order to adjust for

the phase accumulator offset. The units can be either phase accumulator counts or time, with the

relationship that one phase accumulator count is 2−47seconds, or approximately 7.1054 femtoseconds.

The phase accumulator offset between two UXGs can be coarsely measured by comparing their RF OUT

phase at two different frequencies. Measurement accuracy is increased by choosing frequencies that

are farther apart (and thus create larger phase shift), however care must be taken to recognize if the

phase has shifted more than 360⁰. The time offset is related to frequency and phase measured at two

points by the following equation:

ΔTime(seconds) = (

ΔPhase°360°

)

ΔFrequency(Hz)

Figure 9: Coherent Phase Accumulator Time Offset Adjustment (front-panel)



Master System Trigger Source Selection (A.01.15+) In the first release of UXG firmware, only master UXG Trigger2 can be used as the master system trigger

input. In upcoming versions of firmware, several new choices will appear:

BUS – Triggers the system from the *TRG SCPI command.

Trigger Key – Triggers the system when the Trigger hard key on the front panel is pressed.

Trigger 2 – Triggers the system from the external Trigger2 connector.

Timer Trigger – Triggers the system on regular intervals set by a timer.

Figure 10: Multi-Box Sync Master System Trigger Selection



Expanding Beyond Four Boxes Although the first release of UXG firmware only supports a multi-box system of up to four instruments, it

is possible to extend the system to beyond four instruments with additional hardware and/or firmware.

6GHz Clock The UXG 6GHz OUT signal can be passively split up to 8 ways, so it can be distributed to a maximum of 8

instruments. In order to distribute beyond 8 instruments, an amplifier must be used to maintain a

minimum of 5dBm at each UXG’s 6GHz IN connector.

Sync Signal The critical specification of the sync signal is jitter because the sync signal is used to align UXG internals

with a 6GHz clock pulse. It is therefore important that the jitter be less than 83 picoseconds (half of a

6GHz clock pulse).

*Up to 9 UXGs have been daisy-chained in the lab without significant accumulation of jitter. It is

unknown at this time what the limit of daisy-chained instruments is.

Trigger Fan-Out Although the first release of UXG firmware only fans the trigger out to 4 connectors (TRIG3 through

TRIG6), subsequent releases allow an arbitrary number of connectors to be used for fan-out. Thus up to

12 instruments will be able to be triggered by one master UXG (TRIG3 through TRIG14).

Figure 11: Connector Routing For Multi-Box Sync Trigger Fan-Out (A.01.15+)



Daisy-Chaining Trigger Fan-out (A.01.20+)

Introduced in A.01.20 is the ability to daisy-chain the trigger fan-out connection to slave instruments. In

this way, the mater can trigger up to 12 instruments that can trigger a further 12 instruments each (and

so on). Each link in the chain will incur one trigger clock of delay that will need to be accounted for in

LIST or PDWs. To use this feature, route the incoming trigger to a slave’s TRIG1 input and route the

desired slave fan-out connector to Multi-box Sync Trigger:

Figure 12: Multi-box Synchronization Trigger Fan-out Daisy-chaining

Note: The trigger fan-out chain must be synchronized in order and it must be completely synchronized

before any non-fan-out instruments are synchronized.

Example: 4 instruments are daisy-chained for trigger fan-out (A-D), and each instrument then feeds a

rack of 6 instruments (1-6): A->B->C->D 1 1 1 1 2 2 2 2 3 3 3 3 4 4 4 4 5 5 5 5 6 6 6 6

Instruments A, B, C, and D should first be synchronized in that order. The remaining instruments may

then be synchronized in parallel.



Using Active Splitters for Trigger Fan-out

Another method of extending the trigger fan-out is to use an active splitter to buffer one of the master

UXG TRIG3 through TRIG6 outputs:

Figure 13: Externally Buffered Trigger Fan-Out



Input Trigger Metastability Issues (8ns trigger uncertainty) It is possible for the trigger trim algorithm to randomly choose from one of two trim values each time it

is run. This only happens when the incoming trigger pulse is aligned in a particular way relative to the

receiving instrument’s trigger clock. This timing is determined by the propagation delay in the trigger

cable and can be mitigated in the following ways:

1. Adjust the physical length of the cable

2. Adjust the electrical length of the cable by adding output fine delay

3. Perform the trigger trim only once and re-use the same trim value during subsequent

synchronizations.

The third method is recommended as it is the most user-friendly and does not require a lab

measurement to verify. The recommended procedure is as follows:

1. Ensure that MBS Persistent Delays are OFF

a. :MBSync:MASTer|SLAVe:DELay|TRIGger[1]|2:PERSist OFF

b. System->Multi-Box Synchronization->More->Persistent Delays (set both to OFF)

2. Perform a normal synchronization and verify satisfactory results

3. Mark the current delay values as persistent for use in subsequent synchronizations

a. :MBSync:MASTer|SLAVe|DELay:PERSist

b. System->Multi-Box Synchronization->More->Persistent Delays->Persist Delays From

Current Sync

After setting persistent trigger trim delay values, they should be left ON and not adjusted unless cables

are changed and a recalibration is necessary.

Figure 14: Persistent Trigger Trim Delays



Using a System Controller In Place of a Master It is possible to use a system controller to replace all the functionality of the master UXG in a multi-box

system. In this scenario the system controller generates the trigger clock and handles the trigger fan-

out. It may even generate the 6GHz reference clock.

In this configuration, all UXGs are configured as slaves. The master controller must generate a trigger

clock that is routed to each UXG’s 1-250MHz IN connector during the multi-box synchronization process.

All trigger pulses generated by the master controller must be synchronous with this trigger clock, and a

trigger pulse must be generated during the synchronization process after all UXGs are “Awaiting Phase

Reset.”

1. Make the connections per the drawing.

2. On the master controller, output the synchronous trigger clock signal to the UXG slave

instruments.

3. On each slave instrument, press Begin Slave Sync.

4. On each slave instrument, press Await Phase Reset.

5. On the master controller, generate the trigger pulse.

All slave units should display Synchronization Process Complete.

Figure 15: Possible "Masterless" Configuration

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UXG Multi-Box Synchronizationrfmw.em.keysight.com/wireless/helpfiles/n5193a... · UXG Multi-Box Synchronization Keysight Technologies, 2015 Page 4 Definitions System Controller A