BNC AnaPico 875 Installation and operating instructions

Application Note FCP Option (Model 875)
Vector Signal Generator (VSG) Fast Control Port
Purpose
The VSG can now be controlled over an additional port for fast time-critical settings and
data streaming. This application note explains the configuration and usage of the Fast
Control Port option.
Table of Contents
Introduction............................................................................................................................2
FCP Operation Modes ............................................................................................................2
IQ Data Streaming with FCP ...................................................................................................3
Setup FCP for IQ Data Streaming ........................................................................................3
Related SCPI Commands.....................................................................................................3
IQ Stream Timing.................................................................................................................4
SCPI & FCP Example ............................................................................................................5
FCP Input Delay Calibration ................................................................................................5
Step by Step Guide for Calibration...................................................................................6
Required Signals during Calibration ................................................................................6
Selecting Memory Segments..................................................................................................9
Setup for Selecting Memory Segments ..............................................................................9
FCP Segment SCPI Commands ............................................................................................9
Segment Stream Timing......................................................................................................9
SCPI & FCP Example ..........................................................................................................10
FCP Test Mode......................................................................................................................11
Related SCPI Commands...................................................................................................11
FCP IQ Stream in Test Mode .............................................................................................11
FCP Segment Stream in Test Mode...................................................................................13
Cable Assembly ....................................................................................................................14
Further Documentation........................................................................................................14
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Introduction
The fast control port is a parallel port with the possibility for the user to control specific
aspects of the IQ modulation of the VSG. When activated, the FCP can be configured to
operate in one of two main modes. The interface is set to stream either IQ data or memory
segment IDs.
Setting the FCP in the former mode allows the user to directly stream IQ data to the VSG and
thus modulate the carrier frequency, as depicted in Figure 1. The FCP operates source
synchronously and expects to receive IQ data in a single data rate (SDR) along with a clock
thatruns at a stable, predefined rate. Depending on the FCP version and setting, the IQ
modulation is read with a playback rate of 125MSps or 250MSps.
Instead of streaming the IQ modulation data directly through the FCP, the modulation data
can also be replayed from the local VSG IQ memory. When the FCP is configured in segment
mode, it provides the option to choose the replayed IQ data. By streaming the memory
segments IDs of the desired IQ data, the user is thus able to directly switch between the
stored IQ data segments.
Figure 1: Functional diagram of FCP in VSG with non-FCP parts omitted.
FCP Operation Modes
The fast control port (FCP) supports two main use-cases:
•
•
IQ Data streaming to the device for direct IQ modulation
Segment ID streaming to select segments of the internal VSG memory.
To select the operating direction of the Fast Control Port, the FCP must be configured with
the following SCPI commands:
[:SOURce]:FCPort:STReam:SEGment OFF|ON|0|1
Sets the FCP to stream segment IDs.
[:SOURce]:FCPort:STReam:IQ OFF|ON|0|1
Sets the FCP to stream IQ data.
[:SOURce]:BB:ARBitrary:CLOC <freq>
Sets the FCP playback rate when FCP is active.
[:SOURce]:BB:ARBitrary:FCP[:STATe] OFF|ON|0|1
Sets the FCP as a source for the IQ modulation.
Further related commands are documented in the Programmer's Manual[1], and
applicationexamples can be found on the following pages of this application note.
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IQ Data Streaming with FCP
The FCP can be set as an input for IQ modulation data which is then directly applied to
modulate the carrier frequency. To configure the device to receive IQ data on the FCP, the
FCP must be set into IQ streaming mode, and the FCP must additionally be set as the
sourceof the IQ modulation data.
The FCP for the source-synchronously clocked IQ streaming consists of 16 IQ-data bits, a
valid bit, and a clock. The clock is a continuous signal at a fixed frequency with the valid bit
and IQ data transmitted in a single data rate (SDR). The FCP can operate at two different
playback rates, namely.
•
•
125 Mega samples per second with a continuous 250MHz clock
250 Mega samples per second with a continuous 500MHz clock
Please note that some devices only support the 125MSps speed option for FCP. Please check
the specifications for your device or ask your AnaPico representative for details hereof.
Limitations and requirements:
•
•
A stable frequency of 250MHz/ 500MHz is required on the clock pin of the FCP.
Data at the FCP input must be streamed at 125 MSps or 250 MSps SDR.
This is equivalent to the data bits toggling between I and Q every 4ns/2ns,
respectively. Please consult Figure 4 for a graphical representation.
To avoid undesired frequency offset effects, it is recommended to operate the
sender (that drives the clock and the IQ data) andyour VSG at the same reference
clock.
•
Setup FCP for IQ Data Streaming
Configuration steps prior to transmission
1.
2.
3.
Connect an external reference clock (recommended).
Connect the FCP input on the device.
Send stable 125MHz/250MHz clock signal on the FCP connector clock pins
(see electrical specification for details on pin placement)
Complete SCPI command sequence for IQ stream input on FCP:
ROSC:EXT:FREQ<x>
ROSC:SOUR EXT
FREQ <x>
OUTP:STAT <x>
BB:ARB:CLOC <x>
BB:ARB:FCP ON
FCP:STR:IQ ON
Sets the reference frequency (recommended)
Sets the reference to external (recommended)
Sets initial RF output frequency
Sets RF output
Sets the playback rate
Sets FCP as a source of the IQ modulation data
Sets FCP to IQ stream mode
Related SCPI Commands
[:SOURce]:BB:ARB:CLOC <freq>
In FCP mode, this sets the FCP playback rate to <freq>.
Out of FCP mode, this sets the Memory playback rate to <freq>.
*RST value for FCP modes: 125MHz
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[:SOURce]:FCPort:STReam:IQ OFF|ON|0|1
Sets the FCP to stream IQ data.
*RST value: OFF
Figure 2: The FCP:STR:IQ SCPI command determines if the FCP is in IQ streaming mode. The
received data is then forwarded to potentially modulate the carrier frequency. Note that this
mode can only be enabled if all other FCP modes are disabled.
[:SOURce]:BB:ARBitrary:FCP[:STATe] OFF|ON|0|1
Sets the FCP as the source of IQ modulation.
*RST value: OFF
Figure 3: The BB:ARB:FCP[:STAT] command decides if the FCP IQ data is forwarded for IQ
modulation. This command only takes hold if the BB:ARB:WAV:STAT command is disabled.
IQ Stream Timing
Figure 4: IQ stream input timing for the fast control port (FCP) with clock period 𝑇∈{2𝑛𝑠, 4𝑛𝑠}
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The FCP receives a valid signal that is synchronized with the first valid I-data sample,
followed by the first Q-data sample. The valid signal should be driven low during the setup of
the device to ensure proper sampling of I and Q data samples.
The phase relationship of input signals to the FCP are depicted in Figure 4. See the electrical
specifications for details on pin assignment at the MDR 36-pin connector.
Clock and data edges are transferred at the same time. The FCP reads the data upon each
rising edge of the clock. In order to optimize and relax the sampling of the IQ data, the input
delay at the FCP should be calibrated before the first IQ transmission is started. The process
and requirements for calibration are explained in section FCP Input Delay Calibration.
SCPI & FCP Example
This is an SCPI example to set the FCP. Make sure to follow the steps prior to transmission
asdescribed in section Setup FCP for IQ Data Streaming.
ROSC:EXT:FREQ 10e6
ROSC:SOUR EXT
FREQ 50e6
OUTP:STAT ON
BB:ARB:CLOC 125e6
FCP:STR:IQ ON
BB:ARB:FCP ON
Sets the reference frequency to 10 MHz
Sets the reference to external
Sets initial RF output frequency 50 MHz
Enables RF output
Sets the playback rate to 125MHz
Sets FCP to IQ stream mode
Sets FCP as a source of the IQ modulation
data
After successfully configuring the device, the IQ modulation data (e.g., a 1-tone) can be sent
to the FCP - make sure the valid signal is synchronized to the first 16-bit I-data sample. A
valid input IQ stream results in a modulated carrier frequency at the RF output. You can now
•
•
•
Set some frequency with FREQ <x>.
Send another IQ modulation, e.g., 2-tone, to the FCP
input.Watch the output being modulated.
If you have trouble setting up the FCP to correctly receive your IQ data, have a look at
section FCP Test Mode. The FCP IQ streaming comes with an integrated testing mode that
can help detect the most common issues in your setup.
FCP Input Delay Calibration
The FCP has a built-in opportunity to calibrate the input delay for the data ports relative to
the clock port. This feature allows the user to account for signal delays that occur between
the different fast control port pins and thereby optimize the timing of the captured signals.
This optimization is done automatically with a calibration procedure that will be explained
hereafter. During the calibration process, the FCP input delay of each data bit is adjusted
individually.
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Step by Step Guide for Calibration
1.
2.
3.
Startup the device
Physically connect an external reference clock to the VSG device
Lock to the external reference
a. SCPI commands
ROSC:EXT:FREQ <freq> set the external reference frequency
ROSC:SOUR EXT
set the reference clock source to external
b. or use the reference clock tab in the VSG GUI
Physically connect the FCP cable
Send a stable input on the FCP
4.
5.
a.
b.
c.
Stable clock signal of 250 or 500MHz depending on playback rate
Keep valid signal low
Data input: any arbitrary 16-bit signal
6.
Configure the FCP for IQ streaming
a. SCPI commands
BB:ARB:CLOC <freq>
BB:ARB:FCP ON
FCP:STR:IQ ON
set the playback rate (125 or 250MHz)
set the FCP as a source for IQ
modulationenable FCP for IQ streaming
b. Or use the VSG GUI to set the device into FCP IQ streaming mode
Send the required calibration signals (see below for details) on the FCP input port
Start the calibration
a. SCPI command
7.
8.
FCP:STR:CAL 0
start the calibration
The calibration will take several minutes to complete. Please do not modify or disturb the
setup during this process.
Required Signals during Calibration
The same LFSR pattern that is used for the FCP tests is also deployed for the calibration (see
section FCP IQ Stream in Test Mode for related information). To calibrate the FCP input with
your existing setup, please make sure you meet the following requirements for the signals at
the FCP interface.
•
•
•
•
•
•
Stable clock on FCP clock pin
Source synchronous transmission
Pseudo-random pattern at IQ data pins
the signal at valid pin toggling every 2.5-3
secondsMin. 200 valid-high periods
FCP input signals use the same reference clock as the VSG
Stable Clock
The input signal of the clock pin needs to be a stable 250 MHz or 500 MHz, depending on
which playback you intend to use the FCP with. If you would like to use both the 125MSps
and the 250MSps playback rates, please either do a new calibration whenever youswitch the
playback rate or calibrate your FCP input with the faster playback rate.
You need to drive
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•
•
A stable 250MHz at the clock pin for FCP with 125MSps playback rate or
A stable 500MHz at the clock pin for FCP with 250MSps playback rate.
For a proper calibration setup, please make sure the clock signal on the FCP input is
generated with the same reference clock as the reference clock for the VSG. Using an
external reference clock is always recommended for streaming IQ data to the FCP.
Pattern for IQ Data
The IQ data pins of the FCP need to be driven with a predefined pseudo-random pattern. See
the electrical specifications for information on pin placement on the port.
The required I and Q data pattern can be generated with linear feedback shift registers
(LFSR). The following code example describes how the I and Q data are generated.
// initialize I and Q
i_0 = 0x306C;
q_0 = 0xFFFF;
do { // for each iteration.
i
i
i
q
q
q
=
=
=
=
=
=
i
i
i
q
q
q
XOR
XOR
XOR
XOR
XOR
XOR
(i
(i
(i
(q
(q
(q
<<
>>
<<
<<
>>
<<
7);
9);
8);
7);
9);
8);
}
•
For calibration with a 125MSps playback rate, the I and Q data samples are sent
alternatingly, with each new IQ pair representing a new iteration in the above code example.
This will result in a pattern like
i_0 = x306C
i_1 = x696F
i_2 = x5E80
q_0 = xFFFF
q_1 = x7F7F
q_2 = x5F9F
and so forth. Figure 5 depicts how the I and Q data should be sent consecutively.
Please make sure there is a new data sample at every rising clock edge. The data
sample that arrives along with any rising edge of the valid bit must be an I data
sample –not a Q data sample. However, this data sample does not necessarily have
to be the i_0 sample. It can be any i_n sample if the consecutive data sample is the
corresponding q_n sample.
The order of I and Q samples needs to be changed slightly for calibration with a playback rate
of 250 MSps. The sender must generate two pairs of IQ data samples as described in the
above code example. The pairs are then sent to the FCP successively. Figure 6 depicts the
order of the required IQ data, which is
•
i_0 = x306C
i_1 = x696F
i_2 = x5E80
q_0 = xFFFF
q_1 = x7F7F
q_2 = x5F9F
i_0 = x306C
i_1 = x696F
i_2 = x5E80
q_0 = xFFFF
q_1 = x7F7F
q_2 = x5F9F
Similar to the slower playback rate, an I data sample must be sent along with a
rising
edge of the valid signal.
While the valid signal is low, the 16 data pins can be driven with any arbitrary signal. The
data input will thence be considered invalid and inconsequential for calibration.
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Valid Signal
The signal at the valid pin of the FCP (see electrical specifications for pin mapping) must stay
low while the FCP is being enabled. In Figure 5 and Figure 6, the time periods for which the
valid signal is high or low are labeled 𝑡1and 𝑡2respectively. For calibration, these periods are
required to be roughly 3 seconds.
𝑡1, 𝑡2∈[2.3𝑠, 3.5𝑠]
The valid bit must rise from low to high approximately200 times for one whole
calibration to finish.
Reference Clock
It is recommended to have a reference clock that drives both the VSG as an external
reference and all the sender-generated signals of all the FCP signals. If the reference clock is
not locked to both the sender and the VSG, the FCP input calibration may fail due to
frequency offset effects that can not be circumvented.
Required FCP Signals
The following figures each show an example of the signals required at the FCP pins during
calibration. All signals are explained separately and in detail in the preceding subsections.
Figure 5: FCP signals for calibration with 125MSps playback rate and 250MHz clock. Figure not to scale.
Figure 6: FCP signals for calibration with 250MSps playback rate and 500MHz clock. Figure not to scale.
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Selecting Memory Segments
The fast control port (FCP) can be configured to receive memory segment IDs to select
desired memory segments for playback. When the FCP is configured in segment selection
mode, the FCP cannot be configured to run in any other mode simultaneously.
The FCP expects a 16-bit wide memory segment ID, as well as a valid signal that indicates
when a new ID is valid at the FCP.
Setup for Selecting Memory Segments
The configuration steps for segment streaming to FCP are straightforward.
1. Connect the FCP input to the connector on the VSG.
See the electrical specifications section for pin mapping on the connector.
2. Set the FCP to Segment ID stream mode with the SCPI command
FCP:STR:SEG ON
FCP Segment SCPI Commands
[:SOURce]:FCPort:STReam:SEGment OFF|ON|0|1
Sets the FCP to stream segments IDs.
*RST value: OFF
Figure 7: The FCPort:STReam:SEGment command determines whether the FCP is streaming
memory segment IDs. Note that this mode can only be enabled if all other FCP modes
(e.g., stream IQ) are turned off.
Segment Stream Timing
The FCP receives a valid signal that is synchronized with the data. Each new segment ID
needs to be accompanied by a rising edge of the valid signal. The valid signal should be
driven low during the setup of the VSG.
The temporal relationships of the input signals to the FCP are depicted in Figure 4. See the
electrical specifications for details on pin assignment at the connector, where Addr is an alias
for segment ID.
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Segment IDs and valid bit edges are transferred at the same time. The FCP reads the input
with a sampling rate of 250 Mb per second for each signal which naturally limits the
switching of the valid signal to every 4ns at the earliest.
VALID
ADDR
Figure 8: Timing diagram for memory segment inputs (not to scale)
SCPI & FCP Example
1. Write some IQ data to the internal memory of the VSG, e.g., a 1-tone
modulation.This can be done by, e.g., uploading the data of a QI file with the VSG
GUI.
2. You can use either the GUI or the following SCPI commands to further set up
theVSG.
FREQ 50e6
OUTP:STAT ON
BB:ARB:WSEG:SOUR FCP
FCP:STR:SEG ON
BB:ARB:WAV:STAT ON
Sets initial RF output frequency 50MHz
Enables RF output
Sets FCP as a source for segment selection
Sets FCP to segment stream mode
Sets RAM as a source of the IQ modulation
data
After successfully configuring the device, the segment ID can be sent to the FCP - make sure
the positive edge of your valid signal is sent along with the 16-bit segment ID signal. You can
now
•
•
Set some frequency with FREQ <x> on the VSG.
Send a different segment ID with a new positive edge on the valid signal to switch the
IQ modulation data replayed from the RAM.
[Note: The device needs to have stored a waveform with the designated ID you are
sending on FCP, or there will be no modulation waveform to be replayed.]
Watch the output being modulated accordingly.
•
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