ESG/PSG Signal Generator

Output

RF turns the operating state of the RF signal on or off.

Modulation turns on or off all active modulation formats that are applied to the RF output carrier signal of the signal generator.

Signal

Frequency changes the frequency parameter limits as well as the output frequency of the signal generator. The signal generator output frequency is:

Signal Generator Output Frequency = Frequency – Frequency Offset

Minimum Frequency = 100 kHz + Frequency Offset

Maximum Frequency = SigGen Max + Frequency Offset

Frequency is also used during the generate correction routine to set the spectrum analyzer center frequency. Use frequency offset, auto crest factor, and mirror spectrum if there is a frequency translation between the signal generator and the spectrum analyzer.

Frequency Offset alters the visual display on the signal generator and the frequency range limits. It allows the source frequency display to account for a system with frequency translation in it. The frequency offset value is also used by the generate correction function.

The actual output frequency and frequency range limits for the signal generator are offset by the frequency offset value.

Signal Generator Output Frequency = Frequency – Frequency Offset

Minimum Frequency = 100 kHz + Frequency Offset

Maximum Frequency = Signal Generator Max + Frequency Offset

Amplitude sets the signal generator output amplitude. The amplitude value is also used during the generate correction routine to set the spectrum analyzer reference level and attenuator.

The actual output amplitude and amplitude range limits are offset by the amplitude offset:

Signal Generator Output Amplitude = Amplitude – Amplitude Offset

Minimum Amplitude = Signal Generator Minimum + Amplitude Offset

Maximum Amplitude = Signal Generator Maximum + Amplitude Offset

It is not possible to set the maximum amplitude level with the ALC Enable On.

PSG Maximum = 30 dBm, Maximum with ALC Enable = On, 25 dBm

ESG Maximum = 25 dBm, Maximum with ALC Enable = On, 20 dBm

When Attenuator Hold is off, setting the amplitude also sets the ALC level and the attenuator. The ALC level and attenuator value are chosen to keep the ALC level at its optimum level.

When the Attenuator Hold is On, the attenuator value is held constant. Changing the amplitude or ALC level causes the other parameter to change an equal amount. In general, ignoring amplitude offset, the output amplitude is:

Amplitude(dBm) = ALC Level(dBm) – Attenuator Value(dB)

Amplitude Offset applies an offset to the value and range limits of the signal generator amplitude. Use this parameter if there is additional gain or loss between the signal generator and the spectrum analyzer. If there is an amplifier with 10 dB of gain on the output of the signal generator, the amplitude offset should be set to 10 dB. Now all entries to the amplitude value account for this external gain. The amplitude offset value is also used by the generate correction function. The actual output amplitude of the signal generator is:

Signal Generator Output Amplitude = Amplitude – Amplitude Offset

Sample Clock controls the ESG/PSG's Arb Sample Clock setting. This setting is coupled with the Playback Sample Rate setting in the Waveform Setup and playback N5110B Playback Setup tables.

I/Q

I/Q turns the IQ modulation on or off.

Inputs displays the source of the IQ inputs. This information is taken from the hardware configuration and is a read-only feature.

Modulation Filter enables you to select either a 40 MHz lowpass filter in the I/Q signal path before the IQ modulator or a Through path. The 40 MHz filter helps reduce broadband noise and spurs for signals with an 80 MHz or less RF bandwidth. This parameter should be set to Through when using external IQ inputs and signals that have RF bandwidths greater than 80 MHz. The filter has no affect on the PSG Option 015 wide band signal path. The modulator filter value is used by the generate correction function.

Modulation Attenuation Auto determines the mode of modulation attenuation. When set to On, the instrument uses a predefined Modulation Attenuation value for best performance. When set to Off, the instrument uses the value set in the Modulation Attenuation field.

Modulation Attenuation enables you to adjust the attenuator to optimize signal performance at the RF output. The modulator attenuator is an electronic attenuator in the IQ path before the IQ modulator. When ALC is on, the RF output amplitude will not change while the attenuator value is changed until the ALC range is exceeded. The modulator attenuator value is used by the generate correction function.

Changing the IQ modulator attenuator after applying corrections can degrade the image correction. The degradation occurs because the delay through the two attenuators (one for I and one for Q) may not remain constant. If this degradation is observed, try changing the modulator attenuator a few tenths of a decibel (dB) in 0.1 dB steps.

I/Q Scaling adjusts the amplitude of both I and Q outputs while the waveform is playing. Use this setting to attain better ACP and to optimize dynamic range without overdriving the I and Q D/A converters.

I/Q Scaling is preset to 70%. In most cases, this setting provides good dynamic range without overdriving the I and Q DACs. Increasing the I/Q scaling value beyond 70% increases the risk of DAC over-range errors. If an error occurs at the signal generator, reduce the I/Q Scaling value until errors no longer occur.

I/Q Adjustments turns the IQ adjustments on or off.

I Offset applies a DC offset to the I signal before the IQ modulator. It can be used to help minimize carrier leakage or to introduce calibrated impairments.

Q Offset applies a DC offset to the Q signal before the IQ modulator. It can be used to help minimize carrier leakage or to introduce calibrated impairments.

Quadrature Skew enables you to adjust the phase angle between the I and Q vectors. When the quadrature skew is zero, the phase angle is 90 degrees. Positive skew increase the angle from 90 degrees while negative skew decreases the angle from 90 degrees.

ALC and Attenuation

The RF output power of the signal generator is constantly monitored and controlled by the automatic leveling control (ALC) circuit. Its purpose is to hold output power at its desired level in spite of drift due to temperature and time.

There are some modulation conditions the ALC circuit cannot handle properly that lead to output level errors. In these conditions, better power level accuracy can be obtained by turning the ALC off and using power search. ALC off is useful with pulse modulation when the pulse width is narrower than two microseconds, and with certain external I/Q modulation.

Pulse modulation is accomplished using a modulator which precedes the ALC detector. The ALC must, therefore, measure a pulsed signal, and it is able to do this if the pulse width exceeds two microseconds. For narrower pulses, set the ALC to off.

With external I/Q modulation, the ALC loop acts to hold the average output power of the signal generator constant, in spite of variations in the I/Q input power (I2 + Q2). Rapid variations of (I2 + Q2) propagate to the output, while slow variations are removed by the ALC loop, with a high-pass corner of 1 kHz. If you do not want this high-pass filtering, set the ALC to off. With ALC off, the I/Q modulation will be DC-coupled. Using power search, power level accuracy is preserved if (I2 + Q2)1/2 = 0.5 Vrms.

ALC turns the automatic level control on or off. It is not possible to set the maximum amplitude level with ALC on.

PSG Max = 30 dBm, Max with ALC on, 25 dBm

ESG Max = 25 dBm, Max with ALC on, 20 dBm

ALC BW enables you to select the ALC loop bandwidth from the drop-down list . The Auto selection lets the signal generator select the bandwidth automatically based on the current signal setup.

Attenuator Hold turns the attenuation hold on or off. When this function is turned on, the attenuator is locked at its current setting to prevent glitches that can occur when the attenuator is changed. You can use this function any time you want to guarantee that there will be no power discontinuity normally associated with the attenuator switching during power adjustments. When this function is turned off, the attenuator is in a dynamic state, and setting the amplitude also sets the ALC level and the attenuator.

Attenuator Setting sets the value of the output attenuator. The attenuator value is used by the generate correction function. The attenuator value can only be set when the Attenuator Hold is on. When the Attenuator Hold is on, the attenuator value is held constant. Changing the amplitude or ALC level causes the other parameter to change an equal amount. The ALC level and attenuator value are chosen to keep the ALC at its most effective level.

ALC Level sets the output power level only using the ALC. When the ALC circuit is on, the output power level is constantly monitored and controlled. When the ALC circuit is off, the output power level is not controlled. The ALC level value is used by the generate correction function.

Do Power Search enables the power search routine. Power search is an internal calibration routine that improves output power accuracy when the ALC is off. A power search is recommended for pulse-modulated signals with pulse widths less than two microseconds.

If you are using external I/Q modulation, the power search routine assumes that the I/Q input level is
= 0.5 Vrms.

Actual output amplitude will scale directly with .

Power Search Mode enables you to select either manual or auto as the power search mode. With the manual selection, power search will not run until the Do Power Search button is pressed. When the selection is auto, power search will run automatically with each change to the RF frequency or power, and with each change to the AM, burst, pulse, or I/Q modulation state.

Power Search Reference enables you to select either fixed CW or a modulated signal from the drop-down menu when doing a power search. The power search reference function is not available when ALC is on.

RF During Power Search enables you to select either normal or minimum to control the output power of the signal generator during a power search routine. When the selection is normal, nothing is done to the output power during the power search. Glitch and power changes may be present during the search. With minimum selected, the output is protected by putting the attenuator to its maximum value during the power search.

Marker Routing

ALC Hold enables you to select a marker for this function. When the specified marker signal is low, ALC Hold is enabled. With ALC Hold enabled, the output power leveling does not respond to changes to the signal amplitude. Selecting Off disconnects all markers from ALC Hold.

ALT Power enables you to select a marker for the alternate amplitude function. When the marker signal is low, the alternate amplitude settings configured on the ESG signal generator are active. Selecting Off disconnects all markers from the alternate amplitude function.

Burst Pulse Mod enables you to select a marker for this function. When the marker signal is high and the marker polarity is positive, the waveform is blanked until an enabled marker is encountered. When the marker polarity is negative, the waveform is blanked when it encounters an enabled marker. Selecting Off disconnects all markers from the Burst Pulse Mod function.