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Output Modulation Block

This topic describes the parameters of the Output Modulation block.

Enable Output Modulation

I/Q Setup

I/Q Modulation On

I/Q Modulation Source

I/Q DC Alignment - Perform Alignment

I/Q DC Alignment - Clear Alignment

Skew Alignment - Perform Alignment

Skew Alignment - Clear Alignment

AM n Setup

AM n On

Type

Source

Depth - Linear

Depth - Exponential

Depth Increment

External Input - Coupling

External Input - Impedance

Function Generator - Frequency

Function Generator - Frequency Increment

Function Generator - Phase Offset

Function Generator - Shape

Function Generator - Shape Ramp Polarity

Function Generator - Duty Cycle

Dual Function Generator - Amplitude Percent

Dual Function Generator - Frequency

Dual Function Generator - Phase Offset 2

Dual Function Generator - Shape

Dual Function Generator - Shape Ramp Polarity

Dual Function Generator - Duty Cycle

Noise Generator - Types

Pulse Setup

Pulse On

Source

External

Polarity

Internal

Source Type

Width

Width Increment

Period

Period Increment

Delay

Delay Increment

Requested Frequency

Requested Frequency Increment

Actual Frequency

On Time

On Time Points

Off Time

Off Time Points

Repetitions

Repetition Points

Clear List

Trigger Mode

Trigger Immediately

Pulse (Video) Output

Pulse (Video) Output State

Sync Trigger

Sync Trigger State

Sync Trigger Width

Sync Trigger Width Increment

Pulse Trigger Source

Enable Output Modulation

Enables or disables the currently active modulation type of the indicated channel. Most modulation types can be simultaneously enabled except FM with ΦM. An annunciator on the signal generator always indicates whether modulation is on or off.

I/Q

Selecting this check box in this row performs the same function as I/Q Modulation On. If you click or tap elsewhere in this row, the I/Q Setup screen appears, allowing you to configure parameters specific to I/Q modulation.

I/Q Modulation On

Enables or disables the I/Q modulation of the RF Output.

I/Q Modulation Source

Selects the I/Q modulation source.

For instruments with Option EXT, selects either an internal or external I/Q modulation source.

• EXTernal: Routes the applied signals from the I and Q input connectors, or -I/+I/-Q/+Q for differential input connectors, to modulate the RF carrier.

• INTernal: Selects the internal baseband generator, the Signal, as the source for the I/Q modulation of the RF carrier.

I/Q DC Alignment - Perform Alignment

Applies to the M9383B VXG-m and M9384B VXG only.

Invokes an I/Q DC alignment. The instrument’s in-band images and LO feedthrough can negatively impact EVM performance. I/Q DC alignment should be performed when you modulate at a new frequency, or the temperature changes by a few degrees from the last time the alignment was performed.

When to use this feature:

Whenever the best possible EVM performance is required or in use cases where DC and image rejection of I/Q modulation impact measurement results. I/Q DC alignment should be used after the instrument has been warmed up or whenever significant room temperature changes occur. It should be run at least once for each frequency the instrument set to. After each alignment is run, the calibration data is cached for each set frequency. This caching allows you to tune from frequency A to frequency B and back to frequency A with the most recent DC-alignment applied. If the instrument is power cycled, it is recommended that you perform these I/Q DC alignments again. You can also empirically determine how often this DC alignment should be performed, based on how sensitive your measurements are and how much temperature variation you observe over time.

I/Q DC Alignment - Clear Alignment

Applies to the M9383B VXG-m and M9384B VXG only.

Returns the I/Q DC Alignment data at the current frequency to the factory default. You can use this when diagnosing signal quality issues. However, it is recommended to simply run the I/Q DC Alignment anew rather than clearing the alignment.

Skew Alignment - Perform Alignment

Applies to the M9383B VXG-m and M9384B VXG only.

Invokes an I/Q Skew alignment. The instrument’s parasitic time delay (skew) between the I and Q channels can vary with time and temperature. I/Q Skew alignment should be performed when the temperature changes by a few degrees from the last time the alignment was performed.

When to use this feature:

Whenever the best possible wideband EVM performance is required (approximately 1 GHz or greater) or in use cases where wideband I/Q skew impacts measurement results. In most cases, the I/Q skew alignment should not be run often. However, the baseband I/Q paths in the VXG signal generator can be temperature sensitive and, depending on the I/Q data being played from the arbitrary waveform generator, there is a self-heating thermal gradient that could occur between the I and Q path. (This is especially true for OFDM-based I/Q waveforms having a bandwidth greater than 1 GHz.) This thermal gradient can result in one to two pico-seconds of time skew at the extreme bandwidth edges of the I/Q modulation. Thermal mitigation techniques have been deployed to minimize this effect, however, you may empirically decide to run this calibrations more often, if needed.

Skew Alignment - Clear Alignment

Applies to the M9383B VXG-m and M9384B VXG only.

Returns the I/Q Time Skew Alignment data to the factory default. You can use this when diagnosing signal quality issues. However, it is recommended to simply run the I/Q Time Skew Alignment anew rather than clearing the alignment.

AM n

The check box in this row performs the same function as AM n On. If you click or tap elsewhere in this row, the AM Setup screen appears, allowing you to configure parameters specific to AM modulation.

AM n On

Enables or disables the amplitude modulation for the selected path.

When ALC is on, AM cannot be turned on.

AM State cannot be turned on when the source of the corresponding AM path (1 or 2) is used and when AM path is on.

Type

Sets the AM type to linear or exponential AM.

• LINear: Selects linear AM type with depth values in units of percent/volt.

• EXPonential: Selects exponential AM type with depth values in units of dB/volt.

Source

Sets the source to generate the amplitude modulation.

• External: Selects an externally applied signal as the modulation Input

• Function 1: Selects function generator 1 as the modulation source.

• Function 2: Selects function generator 2 as the modulation source.

• Dual Function : Selects the dual function generator as the modulation source.

• Noise 1: Selects the noise generator 1 as the modulation source.

• Noise 2: Selects the noise generator 1 as the modulation source.

Depth - Linear

Sets the linear amplitude modulation depth for the selected AM path in percent.

Depth - Exponential

Depth - Exponential

Sets the exponential amplitude modulation depth for the selected AM path in dB.

Depth Increment

Remote command only.

Sets the increment for linear AM depth step.

External Input - Coupling

Sets the coupling for the amplitude modulation source through the selected external input connector.

• AC: This choice will only pass AC signal components. Any DC offset will be removed.

• DC: This choice will pass both AC and DC signal components.

External Input - Impedance

Sets the input impedance for the externally applied AM input

Function Generator - Frequency

Sets the amplitude modulation rate for the waveform on the selected internal function generator.

Sine: 10 MHz

Otherwise: 1 MHz

Function Generator - Frequency Increment

Remote command only.

Sets the step increment for the internal frequency modulation.

Function Generator - Phase Offset

Sets the phase offset (in radians) of the AM signal. The value can be set in degrees as well via both GUI and SCPI.

Function Generator - Shape

Sets the AM waveform type.

Function Generator - Shape Ramp Polarity

Remote command only.

Sets the ramp direction when :AM{1:2}:INTernal:FUNCtion{1:2}:SHAPe is set to RAMP.

Function Generator - Duty Cycle

Sets the duty cycle in percent for Pulse mode.

Dual Function Generator - Amplitude Percent

Sets the amplitude for tones of the internal dual function generator source as a percent of the peak analog modulation amplitude.

Setting the amplitude of one tone automatically set the other tone to make up the remaining amplitude.

Dual Function Generator - Frequency

Sets the frequency of tone 1 (default) or tone 2 of the internal dual function generator source.

Dual Function Generator - Phase Offset 2

Sets the phase offset in degrees or radians of tone 2 in relation to tone 1 of the internal dual function generator source.

Dual Function Generator - Shape

Sets the shape of tone 1 (default) or tone 2 of the internal dual function generator source.

Dual Function Generator - Shape Ramp Polarity

Remote command only.

Sets the ramp direction of the selected tone (1 or 2) of the internal dual function generator source when Dual Function Generator - Shape is set to Ramp.

Dual Function Generator - Duty Cycle

Sets the duty cycle of the internal dual function generator source in percent for Pulse mode.

Noise Generator - Types

Sets the noise type when the AM Source is set to Noise.

Pulse

Pulse modulation of the RF output requires Option PME/PMR.

When pulse modulation is in use, the instrument provides a logic-high output on a connector which can be used to trigger external equipment when the signal generator’s pulse operation has initiated. See STrig (Sync Trigger).

The instrument also provides an output which is logic-high when the RF Output is on and logic-low when the RF Output is off. See Pulse (Video) Output.

For the pulse types that are triggered, the trigger signal is applied as follows, depending on your VXG model:

The checkbox in this row performs the same function as Pulse On. If you click or tap elsewhere in this row, the Pulse Setup screen appears, allowing you to configure parameters specific to Pulse modulation.

Pulse On

Enables or disables pulse modulation.

For the M9484C, when pulse modulation is enabled, I/Q modulation is disabled.

Source

For M9383B/M9384B, sets or returns the source the signal generator uses for pulse modulation of the RF output signal.

External

For M9383B/M9384B. When the Pulse Source is External, a signal provided on the connector below modulates the RF Output.

• Pulse In connector for M9384B

• M9314B Trig 1 connector for M9383B

When the external signal is logic high (TTL high) the RF Output will be on, when the external signal is logic low (TTL low) the RF Output will be off. This logic can be inverted with the Polarity setting.

View image.

Polarity

The polarity of the external TTL signal can be selected. Normal enables the RF Output when the external signal is TTL high, or Inverted enabled the RF Output when the external signal is TTL low.

Internal

The instrument’s internal circuitry provides the pulsing of the RF Output.

Source Type

Sets the pulse type from the choices in the following table.

Width

For Pulse Source Types of Free Run, Adjustable Doublet, Triggered, Triggered Doublet, and Gated, sets the pulse width for the internally generated pulse modulation. The command, used with the UP|DOWN parameters, will change the pulse width by a user-defined step value. Refer to pulse width increment for setting the value associated with the UP and DOWN choices.

Use PWIDth1 with the DOUBlet parameter and PWIDth1 and PWIDth2 with the ADOublet parameter. Refer to internal source type.

The coupling of width is dependent upon the source type, in the following description the Mandatory Off Time is 10 ns:

Free Run:

Constraint: Width ≤ Period – Positive value of Delay – Mandatory Off Time

If the entered value for the Width is > Period – Positive value of Delay – Mandatory Off Time, the Delay is reduced to a minimum of 0 seconds. If the entered value of Width is still larger than the constraint, Width is set to Period – Mandatory Off Time. Thus, if larger values of Width are desired, set the Period value first.

Adjustable Doublet:

Constraint: Delay1 + Maximum(Width1 or (Delay2 + Width2)) + Mandatory Off Time must be ≥ the minimum of one width + Mandatory Off Time, and ≤ 42 seconds

If the entered value for Width1 is > 42 seconds – Mandatory Off Time – the current value for Delay1, Delay1 is reduced.

If the entered value for Width2 is > 42 seconds – Delay1 – Mandatory Off Time – the current value for Delay2, Delay2 is reduced. If the result yields Delay2 of 0 seconds, and the entered Width2 is still larger than allowed, Width2 is limited to the remaining value.

Triggered, Triggered Doublet:

Constraint: Delay + Width + Mandatory Off Time must be ≥ the minimum Width + Mandatory Off Time, and ≤ 42 seconds

If the entered value for Width is > 42 seconds – Mandatory Off Time – the current value for Delay, Delay is reduced.

Gated:

Constraint: Width ≤ Period – Mandatory Off Time

If the entered value for the Width is > Period – Mandatory Off Time, the Width is set to Period – Mandatory Off Time. Thus, if larger values of Width are desired, set the Period value first.

Width Increment

Remote command only.

Sets the step increment for the pulse width. The step value, set by this command, is used with the UP and DOWN choices available in the pulse width command.

Period

For Pulse Source Types of Free Run and Gated, sets the pulse period for the internally generated pulse modulation. The command, used with the UP|DOWN parameters, will change the pulse period by a user–defined step value. Refer to pulse period increment for setting the value associated with the UP and DOWN choices.

The coupling of period is dependent upon the source type, in the following description the Mandatory Off Time is 10 ns:

Free Run:

For positive values of Delay, if the entered value for Period is < current value for Delay + Width + Mandatory Off Time, the Delay is reduced to a minimum of 0 seconds. If the entered Period is still less than Width + Mandatory Off Time, Width is set to the Period – Mandatory Off Time.

For negative values of Delay, if the entered value for Period is < current value for Width + Mandatory Off Time, the Width is reduced.

Gated:

If the entered value for the Period is < the current value for Width + Mandatory Off Time, the Width value is reduced to Period – Mandatory Off Time.

Period Increment

Remote command only.

Sets the step value for the internal pulse period. The step value, set with this command, is used with the UP and DOWN choices available in the pulse period command.

Delay

For Pulse Source Types of Square, Free Run, Pulse Train, Adjustable Doublet, Triggered, and Triggered Doublet, sets the pulse delay for the internally generated pulse modulation. The command, used with the UP|DOWN parameters, will change the delay by a user-defined step value. Refer to pulse delay increment for setting the value associated with the UP and DOWN choices.

The value accepts ns (nanoseconds) to s (seconds) with a resolution of 10 ns.

For Pulse Source Types of Square and Free Run, Delay establishes the point in time where the Sync Trigger is raised relative to the Width: positive Delay values shift Width after Sync Trigger, negative Delay values shift Width before Sync Trigger. For the other pulse source types, Delay establishes the point in time where the Width begins.

Use Delay1 with Pulse Type of Triggered Doublet, and Delay1 and Delay2 with Pulse Type of Adjustable Doublet. Delay2 is valid only when Pulse Type is Adjustable Doublet.

The coupling of delay is dependent upon the source type, in the following description the Mandatory Off Time is 10 ns:

Square:

Constraint: |Delay| ≤ (1/Actual Frequency) – Sync Trigger Width – Mandatory Off Time

If the entered value for the |Delay| is > (1/Actual Frequency) – the current value of Sync Trigger Width – Mandatory Off Time, Sync Trigger Width is reduced, to the limit of minimum Sync Trigger Width. If the entered value for |Delay| is still larger than the constraint, Delay will be clipped. Thus, if larger values of Delay are desired, set the Requested Frequency value first. Note: negative values for Delay must be < - (Sync Trigger Width + Mandatory Off Time).

For positive values of Delay:

Constraint: Delay ≤ (1/2 * 1/Actual Frequency) – Mandatory Off Time

If the entered value for Delay is > (1/2 * 1/Actual Frequency) – Mandatory Off Time, the Delay will be clipped. Thus, if larger values of Delay are desired, set the Requested Frequency value first.

For negative values of Delay:

Constraint: |Delay| ≤ (1/Actual Frequency) – Mandatory Off Time

If the entered value for |Delay| is > (1/Actual Frequency) – Mandatory Off Time, the Delay will be clipped. Thus, if larger negative values of Delay are desired, set the Requested Frequency value first.

Free Run:

Constraint: |Delay| ≤ Period – Sync Trigger Width – Mandatory Off Time

If the entered value for the |Delay| > Period – current value of Sync Trigger Width – Mandatory Off Time, Sync Trigger Width is reduced, to the limit of minimum Sync Trigger Width. If the entered value for |Delay| is still larger than the constraint, Delay will be clipped. Thus, if larger values of Delay are desired, set the Period value first. Note: negative values for Delay must be < - (Sync Trigger Width + Mandatory Off Time).

Pulse Train:

When pulse train trigger mode is Triggered, Delay specifies the time after a trigger is received before the first Pulse Train On Time starts.

When pulse train trigger mode is Free Run or Gated, Delay is not applicable.

Adjustable Doublet:

Constraint: Delay1 + Maximum(Width1 or (Delay2 + Width2)) + Mandatory Off Time must be ≥ the minimum of one width + Mandatory Off Time, and ≤ 42 seconds

If the entered value for Delay1 is > 42 seconds – the current value for Width1 – Mandatory Off Time, Width1 is reduced to the limit of the minimum Width or the sum of Delay2 + Width2.

If the entered value for Delay2 is > 42 seconds – Delay1 – the current value for Width2 – Mandatory Off Time, Width2 is reduced to the limit of minimum Width.

Triggered, Triggered Doublet:

Constraint: Delay ≤ 42 seconds – Width – Mandatory Off Time

If the entered value for the Delay > 42 seconds – current value of Width – Mandatory Off Time, Width is reduced to the limit of minimum Width. If the entered value for Delay is still larger than the constraint, the Delay will be clipped

Delay Increment

Remote command only.

Sets the step increment for the pulse delay. The step value, set by this command, is used with the UP and DOWN choices in the :PULM:INTernal:DELay[1]|2 command.

Requested Frequency

For the Square pulse source type, sets the pulse rate for the internally generated square wave. The command, used with the UP|DOWN parameters, will change the frequency by a user-defined step value. Refer to Requested Frequency Increment for setting the value associated with the UP and DOWN choices.

This value sets the pulse rate of the square wave with a 50% duty cycle.

If the entered value for Requested Frequency affects Actual Frequency such that (1/Actual Frequency) is < current value for |Delay| + Mandatory Off Time, the |Delay| is set to (1/Actual Frequency) – Mandatory Off Time. In addition, if the entered value for Requested Frequency affects Actual Frequency such that (1/Actual Frequency) is < current value Sync Trigger Width + Mandatory Off Time, the Sync Trigger Width is set to (1/Actual Frequency) – Mandatory Off Time.

Requested Frequency Increment

Remote command only.

Sets the step value for Requested Frequency. The step value, set with this command, is used with the UP and DOWN choices in the :PULM:INTernal:FREQuency command.

Actual Frequency

Query only.

The pulse on and off times have a 10 ns resolution, or a periodicity resolution of 20 ns. Therefore, the actual frequency may be different from the value specified in the Requested Frequency.

Pulse Train

Pulse train requires Option 320 and is dependent on already having Option PME/PMR.

Pulse Train establishes a series of pulses to be applied to the RF Output when the trigger condition is met. The pulse train can be 1 to 2047 pulses. When defining the pulse train, the number of pulses is established by the setting with the most elements in the parameter list.

For M9484C, the total of all the On Times and Off Times, including repetitions, must be at least 30 ns for Trigger Mode of Free Run, or 4.010 us for the Trigger Mode of Triggered. Ensure your composition of the Pulse Train is at least this length.

On Time

Sets the pulse on values for the current list of pulse train on times. If this list is shorter than the other lists, then the last element will be repeated as necessary to match the length of the Off Time or Repetitions. The query returns the count of pulse cycle elements in the list of on times.

For M9484C, the total of all the On Times and Off Times, including repetitions, must be at least 30 ns for Trigger Mode of Free Run, or 4.010 us for Trigger Mode of Triggered.

On Time Points

This query returns the count of elements in the list of on times.

Off Time

Sets the pulse off values for the current list of pulse train off times (where the RF will be off). If this list is shorter than the other lists, then the last element will be repeated as necessary to match the length of the On Time or Repetitions. The query returns the count of pulse cycle elements in the list of off times.

For M9484C, the total of all the On Times and Off Times, including repetitions, must be at least 30 ns for Trigger Mode of Free Run, or 4.010 us for Trigger Modes of Triggered or Gate.

Off Time Points

This query returns the count of elements in the list of off times.

Repetitions

Generates a user-defined list of the pulse repetitions. The maximum is a total count of 2047, so a list of "2047,1" would be too long. Lists that are too long will generate an error and only the first 2047 pulses will be played. If this list is shorter than the other lists, then the last element will be repeated as necessary to match the length of the On Time or Off Time list, whichever is longer.

Repetition Points

This query returns the count of elements in the list of repetitions.

Clear List

Sets the list to a single pulse with On Time, Off Time, and Repetitions to their default values.

Trigger Mode

Sets the triggering mode for the Pulse Train feature.

Trigger Immediately

Runs the pulse train once when Pulse Train is turned on and Pulse Train Trigger Mode is Triggered. If the pulse train is already running, neither this button nor SCPI command has any effect.

Pulse (Video) Output

During pulse modulation, when the instrument’s RF Output is on, a logic-high signal is applied to a connector on the instrument. This is also referred to as Pulse Video.

For M9383B:

Options F14 or F20, for channel 1, the connector is M9043A Trig 1

Options F14 or F20 and Option 002, for channel 2, the connector is M9043A Trig 2

Options F32 or F44 the connector is M9323A Trig 1

For M9384B the connector is Pulse Video Out

For M9484C the connector is Event 2

For M9383B/M9384B, the output can be turned on and off. For M9484C, the output is always enabled.

Pulse (Video) Output State

For M9383B/M9384B only. enables or disables the trigger used to output the pulse modulation signal.

Sync Trigger

For Pulse Source Types of Square, Free Run, Pulse Train, Adjustable Doublet, and Triggered, the instrument provides a logic high signal on a connector which can be used to trigger external equipment when the signal generator’s pulse operation has initiated.

For M9383B:

Options F14 or F20 the connector is M9343A Trig 2

Options F32 or F44 the connector is M9323A Trig 2

For M9384B the connector is Pulse Sync Out

For M9484C the connector is Event 1

For M9383B/M9384B, the output can be turned on and off. For M9484C, the output is always enabled.

Sync Trigger State

For M9383B/M9384B only. Enables or disables the pulse modulation synchronization signal. Sync signal is generated at the predefined timing shown in the diagrams for Source Type.

Sync Trigger Width

Defines the width of the synchronization pulse in seconds. The command, used with the UP|DOWN parameters, will change the width by a user–defined step value. Refer to Sync Trigger Width Increment for setting the value associated with the UP and DOWN choices.

The coupling of sync trigger width is dependent upon the source type, in the following description the Mandatory Off Time is 10 ns:

Square:

Constraint: Sync Trigger Width ≤ (1/Actual Frequency) – Mandatory Off time

If the entered value for the Sync Trigger Width is > (1/Actual Frequency) – Mandatory Off Time, Sync Trigger Width will be clipped. Thus, if larger values of Sync Trigger Width are desired, set the Requested Frequency value first.

Free Run, Pulse Train in Free Run:

Constraint: Sync Trigger Width ≤ Pulse Period – Mandatory Off Time

If the entered value for the Sync Trigger Width is > the current value for the Period – Mandatory Off Time, Sync Trigger Width will be clipped. Thus, if larger values of Sync Trigger Width are desired, set the Period value first.

Adjustable Doublet, Triggered, and Pulse Train in Triggered:

Constraint: Sync Trigger Width ≤ 42 seconds – Mandatory Off Time

Sync Trigger Width Increment

Remote command only.

Sets the step increment for the sync width. The step value, set by this command, is used with the UP and DOWN choices available for Sync Trigger Width.

Pulse Trigger Source

For M9484C only. The pulse trigger is connected to the selected trigger source when pulse is on. If a connector is routed to an output when the pulse feature is turned on with an external source with a pulse type besides Square, Free Run, or Pulse Train, then the output will be disconnected, and the pulse input will be operational. An error will be reported when this happens. (See Trigger Connectors.)