Open topic with navigation

Overview of Keysight M320xA PXIe AWGs and Theory

Keysight M3201A/M3202A PXIe Arbitrary Waveform Generators include an embedded Function Generator (FG), Arbitrary Waveform Generator (AWG), and modulator blocks; together, they form a powerful signal generator that is capable of generating standard waveforms (sinusoidal, triangular, square, and DC voltages) or arbitrary waveforms defined by the user and stored on its onboard RAM. With embedded modulator blocks, the output channels can be modulated in phase, frequency, amplitude, or IQ to create analog or digital modulation.

Working with Signal Generation/Channel Structure

Each channel (Channel 1 to Channel n) has an identical structure that contains a Function Generator (FG), Arbitrary Waveform Generator (AWG), Frequency and Phase Angle Modulator, Amplitude and DC Offset Amplitude Modulator, and an IQ Modulator.

Channel Numbering and Compatibility Mode

Compatibility mode, can be changed by open, is available to support legacy modules and allows the channel numbering (channel enumeration) to start with either
CH0 or CH1.

Channel Waveshape Types

Each channel has a Function Generator (FG) block that generates basic periodic signals and an Arbitrary Waveform Generator (AWG) block that generates arbitrary waveforms.

• Signal Generation with the Function Generator
• Signal Generation with the Arbitrary Waveform Generator

* Only available for Keysight M3202A PXIe AWG models

Programming Information

Signal Generation with the Function Generator

Each channel has a Function Generator (FG) that generates basic periodic signals (sinusoidal, triangular, square, etc.) and is commonly used to generate the RF carrier in modulation schemes. These periodic signals can be modulated in frequency, phase, amplitude, or IQ.

Signal Generation with the Arbitrary Waveform Generator

Each channel has an Arbitrary Waveform Generator (AWG) block that generates arbitrary waveforms that can be sent directly to each output channel or they can be used as a modulating signal for the frequency, phase, amplitude, or IQ modulators.

See Working with AWG Waveforms.

Channel Frequency and Phase

Each channel has an Angle Modulator block that has a frequency and phase control.

In angle modulation schemes, these controls set the frequency and phase of the carrier. See Frequency and Phase Modulation (Angle Modulator Block).

Programming Information

Channel Amplitude and DC Offset

Each channel has an Amplitude Modulator block that has an amplitude and DC offset control; these controls have a combined range from 1.5 V to –1.5 V.

See Frequency and Phase Modulation (Angle Modulator Block).

Programming Information

Working with AWG Waveforms

Each channel has an Arbitrary Waveform Generator (AWG) block that generates arbitrary waveforms.

This section describes the following topics:

• AWG Programming Process
• AWG Waveform Queue System
• AWG Prescaler and Sampling Rate
• AWG Trigger Mode
• AWG External Trigger Source
• AWG External Trigger Behavior
• AWG Markers
• AWG FlexCLK Synchronization (models with variable sampling rate)
• AWG Waveform Array and *.cvs File Structure
• AWG Waveform Types

AWG Programming Process

AWG block operation can be configured with a one-step programming process
or with a step-by-step programming process.

One-Step AWG programming process

• The possibility to prepare the AWG queue with multiple waveforms in advance before starting the generation; this may be important to create more complex generation sequences.
• The possibility to have a variety of waveforms in the onboard RAM in order to queue them repeatedly in the AWGs in an efficient way.
• The precise moment when waveforms are transferred from a file to the PC RAM and to the onboard RAM. This may be important for long waveforms and time-critical applications.

Step-by-Step AWG programming process

1. Create waveforms in the PC RAM
   with new ; waveforms can be created from points in an array
   or from points in a file stored on hard disk.
2. Transfer waveforms to a module's onboard RAM with waveformLoad .
3. Queue waveforms in an AWG with AWGqueueWaveform to create the desired generation sequence.
4. Select the sync mode of the queue with AWGqueueSyncMode .
5. Start the generation with AWGstart and provide triggers if required.
   See AWG Waveform Queue System .

AWG Waveform Queue System

Each AWG block has a flexible waveform queue system that can be used to configure complex generation sequences. In order to generate waveforms, they must be loaded into the module onboard RAM and queued in each corresponding AWG.

The AWG waveform queue system has the following advantages:

• Provides a way to generate a sequence of waveforms:
  one after the other with no discontinuities.
• Allows selection of many parameters: (trigger mode, start delay, cycles,
  prescaler, etc.) individually per queued waveform.
• Waveforms can have many instances in many AWG queues: but only one copy is required in the onboard RAM; this feature saves onboard RAM memory.

Each AWG queued waveform has the following parameters:

• Trigger Mode: selects the trigger for the waveform.
• Start Delay: adds an optional delay from the reception of the trigger to the beginning of the waveform generation.
• Cycles: the number of times the waveform is repeated. Using the right trigger mode, the AWG can be set to require one trigger per cycle or just one trigger at the beginning of all cycles.
• Cyclic Mode: sets the repetition cycles for the complete queue. The default mode is one shot: the complete queue will be reproduced one time. Complete queues with a number of waveforms with a limited number of cycles can be repeated with AWGqueueConfig .
  • For Cyclic mode, the minimum play time per cycle should be 1 µs for M3201A/M330xA and 2 µs for M3202A modules.
  • For fast trigger rates, it is recommended to consolidate all waveforms into a single bigger waveform.
• Prescaler: divides the effective waveform sampling rate.
  See AWG Prescaler and Sampling Rate .

AWG Waveform Queue System Examples

Inter-waveform/inter-cycles discontinuities: The AWG Queue System allows the user to queue many waveforms one after the other. It also provides the capability to set repetition cycles per waveform and repetition cycles for the complete queue. In all these cases, there are absolutely no discontinuities between waveforms or cycles, providing a continuous waveform generation from the last sample point of the finished waveform to the first sample point of the starting waveform.

AWG Prescaler and Sampling Rate

The user can set a different prescaler value for each of the waveforms queued in the AWG. This prescaler reduces the effective sampling frequency of each individual waveform as follows:

M3201A

0 => fs=500 MS/s

>=1 => fs=100/n MS/s

M3202A

0 => fs=1 GS/s

1 => fs=200 MS/s

>1 => fs=100/n MS/s

where:

• f_s is final effective sampling frequency.
• prescaler is an integer value (0 to 4095).

An important advantage of this method is the possibility to change the sampling frequency in real time from one waveform to another, reducing waveform sizes and maximizing the flexibility of the AWG.

AWG Trigger Mode

A different trigger mode can be configured in each queued waveform.

1 VIHVITRIG is equivalent, but is considered obsolete

Programming Information

If the queued waveforms are going to use any of the External Trigger modes, the source of this trigger must be configured using AWGtriggerExternalConfig . The available external trigger options.

AWG External Trigger Source

AWG External Trigger Behavior

AWG Markers

A different marker can be configured for each AWG channel. All waveforms must already be queued (AWGqueueMarkerConfig ) in one of the module's AWGs.

AWG FlexCLK Synchronization
(models with variable sampling rate)

FlexCLK Technology (models w/ variable sampling rate) shows the internal diagram and the operation of the M3201A/M3202A PXIe AWGFlexCLK system. This advanced technology allows you to change the sampling frequency of the AWGs (CLKsys), while maintaining full synchronization capabilities due to the internal CLKsync signal.

CLKsync is an internal signal used to start the AWGs and it is aligned with CLKsys and PXI CLK10. Its frequency depends on the FlexCLK Technology (models w/ variable sampling rate), resulting in the following scenarios:

f_CLKsync = f_{PXI CLK10}

When both frequencies coincide, there is no phase uncertainty between both signals and a trigger synchronized with PXI CLK10 will start the AWGs always with the same skew, independently of the clock boot conditions. This ensures proper synchronization between different modules.

f_CLKsync! = f_{P XI CLK10}

When both frequencies do not coincide, both signals are still aligned, but there is a phase uncertainty due to their frequency difference. In this case, if a trigger synchronized with PXI CLK10 is sent to the system, there might be a skew between the start of different AWGs.

This phase uncertainty can be easily corrected using clockResetPhase . This function sets the modules in a sync mode and the next trigger is used to reset the phase of the CLKsync and CLKsys signals, not to start the AWGs. In this way, the phase uncertainty between different modules or between different boot conditions can be eliminated, resulting in a predictable and repeatable skew.

AWG Waveform Array and *.cvs File Structure

The two possible sources of waveforms are an array in the PC RAM and a file in the PC HDD. The memory array is just an array of waveform points, without header and without any particular structure. A waveform file is simply a text file with values separated by commas (*.csv).

The waveformType is a parameter that tells the module which kind of waveform it used to configure the AWG internally.

AWG Waveform Types

See waveformType in waveform file or in new .

Working with Signal Modulation

Signals can be modulated in frequency, phase, amplitude, or IQ.

• Frequency and Phase Modulation (Angle Modulator Block)
• AM and DC Offset (Amplitude Modulator Block)
• IQ Modulation (Quadrature Modulator Block)

Frequency and Phase Modulation (Angle Modulator Block)

The output signal of the Function Generator (FG) block or the Arbitrary Waveform Generator (AWG) block can be modulated.

*Models with Option DM1 dual modulation capability (amplitude and angle modulation simultaneously)

The modulating signal is generated using the AWG associated to that particular channel, for example, AWG1 for channel 1. The angle modulator allows the user to create any analog/digital frequency or phase modulation, for example: FM, FSK, PM, PSK, DPSK, etc.

The output signal of a channel using the frequency modulation is the following:

where:

• A is the channel amplitude (set by channelAmplitude )
• G is the deviation gain or peak frequency deviation
  (set by modulationAngleConfig ). G is only used for 16-bit waveforms.
• AW G(t) is the normalized modulating signal generated by the AWGs
• cos(2πf_ct+ϕ_c) is the carrier signal, generated with the
  Function Generators

As an example, for the generation of an FM signal with an amplitude of 0.8 Vp, a modulation index (h) equal to 0.5 and a maximum frequency of the modulating signal of 10 MHz, the settings must be A=0.8 and G=5,000,000 (G = h*maxf req[AW G(t)]).

The output signal of a channel using the phase modulation is the following:

where:

• A is the channel amplitude (set by channelAmplitude )

• G is the deviation gain or peak frequency deviation
  (set by modulationAngleConfig ). G is only used for 16-bit waveforms.
• AW G(t) is the normalized modulating signal generated by the AWGs

• cos(2πf_ct+ϕ_c) is the carrier signal, generated with the
  Function Generators

As an example, for the generation of a PM signal with an amplitude of 0.8 Vp and a modulation index (h) equal to 1800, the settings must be A=0.8 and G=180 (G=h).

Programming Information

AM and DC Offset (Amplitude Modulator Block)

The amplitude modulator can be used to modulate the amplitude or change the DC offset of the output signal.

The modulating signal is generated using the AWG associated with a particular channel (for example, AWG1 corresponds to Channel 1). The Amplitude Modulator can be used to create analog/digital amplitude modulation (for example, AM, ASK, etc.).

The output signal of a channel using the Amplitude Modulator is the following:

where:

• A is the channel amplitude (set by channelAmplitude ).

• G is the deviation gain (set by modulationAmplitudeConfig ). G is only used for 16-bit waveforms.
• AWG(t) is the normalized modulating signal generated by the AWG.

• cos(2πf_ct+ϕ_c) is the carrier signal, generated with the
  Function Generators

As an example, for generation of an AM signal with an amplitude of 0.8 Vp and a modulation index (h) equal to 0.5, the settings must be A=0.8 and G=0.32 (G = h ∙A²).

The output signal of a channel using the amplitude modulator to modulate the offset is the following:

Options

Programming Information

IQ Modulation (Quadrature Modulator Block)

The output signal of the Function Generator can be modulated simultaneously in amplitude and angle (frequency or phase). This allows the creation of an IF signal with amplitude modulation while the frequency is scanned.

However, the most common use of dual modulations is the amplitude and angle modulation decomposed to in-phase (I) and quadrature (Q) components, commonly known as IQ modulation. In order to make the creation of IQ modulations easier, there are dedicated programming functions for that purpose.

The modulating signals are generated using the IQ Modulation (Quadrature Modulator Block) associated to that particular channel, for example, AWG1 for channel 1. In this case, the waveform loaded into the AWG is composed by the two waveforms (for example, I and Q components, see AWG FlexCLK Synchronization (models with variable sampling rate)).

The output signal of a channel using the IQ modulator is the following:

where:

• A is the channel amplitude (set by channelAmplitude ).

• AWG_I(t) and AWG_Q(t) are the normalized modulating signals generated by the AWGs.

• cos / sin(2πf_ct + ϕ_c) is the carrier signal, generated with the Function Generator. It is also possible to use the IQ modulator with amplitude and phase components:

where:

• A is the channel amplitude (set by channelAmplitude ).

• AWG_A(t) and AWG_ϕ(t) are the modulating signals generated by the AWGs.

• cos(2πf_ct + ϕ_c) is the carrier signal, generated with the Function Generators.

Mathematical Background of IQ Modulation

where the I and Q components are defined as follows:

and the IQ components become very useful to set the amplitude (A) and the phase(ϕ) of the output signal, resulting in IQ modulation (or QAM, Quadrature Amplitude Modulation).

Programming Information

Working with I/O Triggers

The M3201A/M3202A PXIe AWG has general purpose input/output triggers
(TRG connectors/lines). A trigger can be used as a general purpose digital IO or as a trigger input, and can be sampled using the options shown below in
Trigger Synchronization/Sampling Options.

Working with the Clock System

The M3201A/M3202A PXIe AWG uses an internally generated high-quality clock (CLKref) which is phase-locked to the chassis clock. Therefore, this clock is an extremely jitter-cleaned copy of the chassis clock. This implementation achieves a jitter and phase noise above 100 Hz which is independent of the chassis clock, depending on it only for the absolute frequency precision and long term stability.
A copy of CLKref is available at the CLK connector.

CLKref is used as a reference to generate CLKsys, the high-frequency clock used to sample data.

CLK Output Options

FlexCLK Technology (models w/ variable sampling rate)

The sampling frequency of the M3201A/M3202A PXIe AWG (CLKsys frequency) can be changed using the advanced clocking system.

FlexCLK System

where:

• CLKref is the internal reference clock, and is phase-locked to the chassis clock.
• CLKsys is the system clock, used to sample data.
• CLKsync is an internal clock used for the synchronization features of the M3201A/M3202A PXIe AWG.
• PXI CLK10 is the 10 MHz clock of the PXI/PXIe backplane.

The CLKsys frequency can be changed within the range indicated in the datasheet of the corresponding product (clockSetFrequency (Requires Option CLV) ). The CLKsync frequency changes with the CLKsys frequency as follows:

The CLKsync frequency is returned by clockSetFrequency (Requires Option CLV) .

CLKref Frequency in AWG Modules with Option CLV

In M3201A-CLV modules, CLKref frequency (freqCLKref) changes as follows, as a function of CLKsys frequency (freqCLKsys):

• Between 400 MHz and 500 MHz => freqCLKref = freqCLKsys/40
• Between 300 MHz and 400 MHz => freqCLKref = freqCLKsys/30
• Between 200 MHz and 300 MHz => freqCLKref = freqCLKsys/20
• Between 150 MHz and 200 MHz => freqCLKref = freqCLKsys/15
• Between 100 MHz and 150 MHz => freqCLKref = freqCLKsys/10
• Below 100 MHz => error

In M3202A-CLV modules, CLKref frequecy (freqCLKref) changes as follows, as a function of CLKsys frequency (freqCLKsys):

• Between 800 MHz and 1000 MHz => freqCLKref = freqCLKsys/80
• Between 600 MHz and 800 MHz => freqCLKref = freqCLKsys/60
• Between 400 MHz and 600 MHz => freqCLKref = freqCLKsys/40
• Below 400 MHz => error