External Triggering 2-Way Communication
Frequency & Power Sweep Measurement
Using Agilent N1911A and N1912A
P-Series Power Meters
Application Brief
Introduction
This application note applies
to the following products
from Agilent Technologies:
• N1911/12A P-Series
power meter
• Agilent power sensors
In many cases, power meters and power sensors are used for system calibration in manufacturing. During system calibration, frequency sweep or power sweep needs to be carried out to
compensate for errors or system losses. Sometimes this extends test time, depending on the
number of system calibration points used to complete the process.
Conventionally, a signal generator is used as a source and the power meter is connected to the
system for system calibration. The signal generator steps thru frequency/power with constant
power/frequency. The power meter is set to the frequency based on the signal generator and
captures a measurement. This process continues until the end of the frequency/power step
point. Completing one system calibration in manufacturing extends test time. To shorten the
test time, a new firmware enhancement included in P-series power meters allows users to
speed up the measurement or calibration using an external triggering capability. This feature
performs the frequency/power sweep automatically with signal source and synchronizes
through hardware triggering.
This application note demonstrates the capability of the Agilent Technologies N1911A/12A
P-Series power meter to perform the external triggering 1-way and 2-way communication
frequency and power sweep measurements. In the provided procedures [ ] indicates command
keys on the instrument’s front panel and bold text indicates a softkey or selection choice on the
instrument’s screen.
Frequency Sweep Mode
Frequency Sweep mode is used in a frequency response calibration system where the amplitude is constant and the frequency of the power source signal is swept. This mode can be used
to determine the frequency response of a device under test (DUT).
Table 1. Procedures to configure the N1911A/12A power meter for frequency sweep mode
Step
Procedures
1
Connect the power sensor to the signal generator/signal source
2
Connect the power meter TRIG OUT to the signal source TRIG IN using
a BNC cable. The same connection is applied between the signal source
TRIG OUT and the power meter TRIG IN
3
Press [Channel] on the power meter. Set the Sensor Mode to AVG Only
4
Press [Trig/Acq] on the power meter, Acqn and select either Sing Trig or
Cont Trig
5
Press Settings>Source>Ext to set the trigger source to external
6
Press 1 of 2>Output>On to allow the TTL level high to be produced at
TRIG OUT
7
Set the trigger buffer size by sending the SENSe:BUFFer:COUNt <buffer_
size> command to the meter through SCPI
8
Press [Channel] or [Meas] on the power meter to configure the
measurement settings such as averaging, measurement frequency, offsets,
and duty cycle
9
Set the frequency range and step by sending the below commands through
SCPI:
• SENSe:FREQuency:STARt <start_frequency><frequency_unit>
• SENSe:FREQuency:STOP <stop_frequency><frequency_unit>
• SENSe:FREQuency:STEP <frequency_step_size>
10
Send an *OPC command to the power meter
11
Set the power meter to Continuous Trigger mode by sending the
INITiate:CONTinuous ON command
12
Configure and set the required power sweep range and step on the signal
source accordingly
13
Set the signal source trigger input and trigger output, then start sweeping
14
Poll the status of the power meter by sending an *ESR?. *ESR will return
1 when buffering is completed. Use FETCh? to retrieve all buffered
measurements
2
Power Sweep Mode
Power Sweep mode is used in a power level calibration setup when the frequency is constant
(CW frequency) and the amplitude of the power source signal is swept. This mode can be used
to characterize the flatness, linearity, or gain compression of a DUT.
Table 2. Procedures to configure the N1911A/12A power meter for Power Sweep mode
Step
Procedures
1
Connect the power sensor to the signal generator/signal source
2
Connect the power meter TRIG OUT to the signal source TRIG IN using a
BNC cable. The same connection is applied between the signal source TRIG
OUT and the power meter TRIG IN
3
Press [Channel] on the power meter. Set the Sensor Mode to AVG Only
4
Press [Trig/Acq] on the power meter, Acqn and select either Sing Trig or
Cont Trig
5
Press Settings>Source>Ext to set the trigger source to external
6
Press 1 of 2>Output>On to allow the TTL level high to be produced at TRIG
OUT
7
Press Slope and select + or – to set the trigger edge
8
Set the trigger buffer size by sending the SENSe:BUFFer:COUNt <buffer_
size> command to the meter through SCPI
9
Press [Channel] or [Meas] on the power meter to configure the
measurement settings such as averaging, measurement frequency, offsets,
and duty cycle
10
Send an *OPC command to power meter
11
Set the power meter to Continuous Trigger mode by sending the
INITiate:CONTinuous ON command
12
Configure and set the required power sweep range and step on the signal
source accordingly
13
Set the signal source trigger input and trigger output, then start sweeping
14
Poll the status of the power meter by sending an *ESR?. *ESR will return
1 when buffering is completed. Use FETCh? to retrieve all buffered
measurements
3
One-Way External Triggering Communication
The signal source’s TRIG OUT is connected to the power meter’s TRIG IN (see Figure 1). Then
the Start, Stop, and Step frequencies are set for the signal source and power meter. Once the
sweeping operation starts, the signal source steps through the frequency points and outputs
a trigger signal to the power meter at every step for synchronization purposes. Only 1-way
synchronization occurs during this process, which is from the signal source to the power meter.
A proper dwell time has to be setup in the signal source to ensure the measurement readings
of the power meter are settled before stepping through to the next frequency point. At the end
of the frequency step the FETCH? command is used to retrieve all the buffered readings at once.
This same process applies for power step. The buffer memory of power meter is a maximum of
2,048 readings.
BNC cable
Trig In
Trig out
ESG signal source
Figure 1. One-way communication
external triggering setup diagram
Power sensor
P-Series power meter
Two-way External Triggering Communication
To set up a 2-way external triggering communication, where the trigger output enables the
mode’s 2-way handshake, the signal source’s TRIG OUT is connected to the power meter’s
TRIG IN. The power meter’s TRIG OUT is connected to the signal source’s TRIG IN (see Figure
2). Then the Start, Stop, and Step frequencies are set for the signal source and power meter.
Once the sweeping operation begins the signal source steps to the first frequency point and
generates a trigger output signal to the power meter, the acquisition begins. After the measurement reading is settled and stored, the power meter outputs a trigger signal back to the signal
source to continue with the next frequency step. The sequence is repeated for every frequency
step. With this method, there is synchronized communication in 2-way hardware triggering and
setting the correct dwell time on the signal source is not required. At the end of the frequency
step the FETCH? command is used to retrieve all of the buffered readings at once.
BNC cable
Trig in
Trig in
Trig out
Trig out
ESG signal source
Figure 2. Two-way communication
external triggering setup diagram
Power sensor
4
P-Series power meter
External triggering 2-way frequency sweep measurement
Use the following SCPI commands for external triggering 2-way frequency sweep measurement.
Table 3. Procedures to configure the N1911A/12A power meter for Power Sweep mode
SCPI
Description
Agilent ESG/MXG/PSG signal generator
SYST:PRES
Preset the instrument to its default settings
OUTP:STAT ON
Turn on RF output
LIST:TYPE STEP
Enable the frequency/power sweep list
INIT:CONT OFF
Select to single list or step sweep
FREQ:START 50MHz
Set start frequency to 50 MHz (example)
FREQ:STOP 6000MHz
Set stop frequency to 6000 MHz (example)
SWEEP:POINTS 596
Set frequency sweep points to 596 (example)
POWER:LEVEL 5DBM
Set output power level to 5 dBm (example)
TRIG:SOURCE BUS
Enable GPIB triggering using the *TRG command
LIST:TRIG:SOUR EXT
Enable the triggering of a sweep event by an externally applied at the TRIGGER IN connector
LIST:DWEL:TYPE STEP
Select the dwell time from the step sweep
POWER:MODE FIX
Stop a power sweep. Enable signal source to operate at a fixed power level
FREQ:MODE LIST
Select the Swept Frequency mode
Agilent P-Series power meter
SYST:PRES
Preset the instrument to its default settings
SENS:DET:FUNC AVERAGE
Set measurement mode to average for CW\average power measurement
TRIG:SOUR EXT
Set to external triggering which is require for frequency sweep operation
OUTP:TRIG EXT
Set power meter trigger output to external triggering
OUTP:TRIG ON
Enable trigger output port
SENS:AVER:COUNT 1
Set average count to 1 (example)
SENS:MRATE DOUBLE
Set measurement speed to Double (example) to speed up the measurement
SENS:BUFF COUNT 596
Set buffer count to 596 (example)
SENS:FREQ:START 50MHz
Set start frequency to 50 MHz (example)
SENS:FREQ:STOP 6000MHz
Set stop frequency to 6000 MHz (example)
SENS:FREQ:STEP 596
Set frequency step to accept 596 steps (example)
INIT:CONT ON
Set to Free Run mode to accept continuous trigger cycles
*OPC
Enable the operation complete command and set the operation complete bit in the Standard Event Status
Register when all pending device operations have completed
Wait 1 sec
Agilent ESG/MXG/PSG signal generator
INIT
Initialize the signal source
*TRG
Trigger the device if BUS is the selected trigger source
Agilent P-Series power meter
*ESR?
Poll the status of the power meter by sending *ESR?. *ESR will return 1 when buffering is completed
FETCH?
Use FETCh? to retrieve all buffered measurements
5
External triggering 2-way power sweep measurement
Use the following SCPI commands for external triggering 2-way power sweep measurement.
Table 4.
SCPI
Description
Agilent ESG/MXG/PSG signal generator
SYST:PRES
Preset the instrument to its default settings
FREQ 1000MHz
Set frequency to 1000 MHz (example)
OUTP:STAT ON
Turn on RF output
LIST:TYPE STEP
Enable the frequency/power sweep list
INIT:CONT OFF
Select to single list or step sweep
POWER:START -20DBM
Set start power to –20 dBm (example)
POWER:STOP 10DBM
Set stop power to 10 dBm (example)
SWEEP:POINTS 121
Set power sweep points to 121 (example)
TRIG:SOURCE BUS
Enable GPIB triggering using the *TRG command
LIST:TRIG:SOUR EXT
Enable the triggering of a sweep event by an externally applied signal at the TRIGGER IN
connector
LIST:DWEL:TYPE STEP
Select the dwell time from the step sweep
POWER:MODE LIST
Select the Swept Power mode
POW:ATT:AUTO ON
Enable the signal source’s automatic loop control (ALC) to adjust the attenuator so that at a
specified RF power level the signal source’s RF output connector is maintained
FREQ:MODE FIX
Select the stop frequency sweep and allow signal source to operate at a set frequency sweep
Agilent P-Series power meter
SYST:PRES
Preset the instrument to its default settings
SENS:FREQ 1000MHz
Set frequency to 1000 MHz (example)
SENS:DET:FUNC AVERAGE
Set Measurement mode to average for CW\average power measurement
TRIG:SOUR EXT
Set to external triggering which is required for the frequency sweep operation
OUTP:TRIG EXT
Set power meter trigger output to external triggering
OUTP:TRIG ON
Enable the trigger output port
SENS:AVER:COUNT 1
Set average count to 1 (example)
SENS:MRATE DOUBLE
Set measurement speed to Double (example) to speed up the measurement
SENS:BUFF COUNT 121
Set buffer count to 121 (example)
INIT:CONT ON
Set to Free Run mode to accept continuous trigger cycles
*OPC
Enable operation complete command and set the operation complete bit in the Standard Event
Status Register when all pending device operation have completed
Wait 1 sec
Agilent ESG/MXG/PSG signal generator
INIT
Initialize the signal source
*TRG
Trigger the device if BUS is the selected trigger source
Agilent P-Series power meter
*ESR?
Poll the status of the power meter by sending *ESR?. *ESR will return 1 when buffering is
completed
FETCH?
Use FETCh? to retrieve all buffered measurements
6
Comparison of 1-way and 2-way
External Triggering
In 1-way or 2-way external trigger measurement, measurement data is stored in the buffer
and the FETCH? command is used to retrieve all the buffered readings at one time. While this
method for obtaining data requires more programming or coding, it provides faster measurement speed. One-way external triggering requires proper dwell time for the signal generator in
order to let the power meter measurement settled before the signal generator proceeds to next
frequency point. This extends measurement speed due to the dwell time.
Table 5. Pros and cons of conventional, 1-way and 2-way external triggering frequency/power sweep
measurement
Method
Pros
Cons
Conventional
Less programming/coding
Longer test time
1-way external
triggering
Faster test time than
conventional method
More programming/coding.
Requires dwell/wait time for
signal generator
2-way external
triggering
Faster test time than 1-way
external triggering method.
No dwell/wait time for signal
generator and power meter
More programming/coding
Conclusion
With the new enhanced P-Series power meter firmware with external triggering in CW mode,
the measurement test time can be shortened significantly. Speed improvement is noticeable,
especially when there are multiple instruments in a system controlled by a single controller.
This new measurement alternative allows power measurements speed to be optimized to produce a reliable result and meet throughput requirements without incurring any additional cost.
References
Maximizing Measurement Speed using P-Series Power Meter - Application Note
Literature number 5989-7678EN
Practices to Optimize Power Meter/Sensor Measurement Speed and Shorten
Test Times - Application Note, Literature number 5990-8471EN
7
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© Agilent Technologies, Inc. 2013
Published in USA, July 03, 2013
5991-2645EN