Amplitude Control; Computational Time; Internal Eeprom; Modes Of Rf Generation - SIGNALCORE SC5511A Operating & Programming Manual

Amplitude Control

The output level of the SC5511A is controlled through the automatic leveling control (ALC) circuitry. The
ALC can operate in close or open loop. The advantages of the close loop over the open loop operation
are that the power levels are more stable and accurate. The disadvantage of the close loop is that it
increases the AM noise of the carrier sideband. Although this AM noise is typically lower than the phase
noise, it may have impact on some applications. In such applications, it is best to operate the ALC in
open loop. Fine amplitude adjusts can be made by changing the ALC DAC value.

Computational Time

The ALC control is accomplished by controlling the ALC DAC and the output step attenuator. The settings
of these two components are dynamically calculated based on the level required and a large set of
calibration values. Similarly, to change frequency would require four phase lock loops to be
programmed and their settings are dynamically calculated based on a set of calibration values. The
computational effort to compute these settings is great. Typical computational time and setting up for
frequency change is approximately 250 µs, while it is about 350 µs to compute and set up the ALC.
For faster frequency changes, especially for sweeps less than a couple of 100 MHz, it is recommended
that the automatic leveling of the power be turned off. This will prevent the SC5511A from having to
compute a fresh set of the ALC parameters at each frequency point. Typically the un-calibrated power
level does not change by more than a couple of dB over 100 MHz range. See device register 0x14 for
details on turning on and off this automatic leveling feature.

Internal EEPROM

The SC5511A contains an EEPROM whose memory space is divided into calibration and operating data
spaces. The calibration data space contains SC5511A device information such as serial number,
hardware revision, firmware revision, and production date. In addition, this space holds the calibration
data for frequency tuning and amplitude control. The operating data space contains the default startup
configuration of the device such as the single fixed tone mode frequency and sweep/list mode
operation. It also holds the list mode configuration parameters such as sweep behavior (saw or
triangular waveform), software or hardware trigger, start/stop/step frequencies, dwell time, sweep/list
cycles, etc. Space is allocated for 2048 frequency points that the user may choose to store for list mode
operation. The internal EEPROM is not directly accessible for users to store data.

Modes of RF Generation

The SC5511A has both single fixed tone and list mode operation for channel 1. In single fixed tone mode,
it operates as a normal synthesizer where the user writes the frequency (RF_FREQUENCY) register to
change the frequency. In list mode, the device is triggered to automatically run through a set of
frequency points that are either entered directly by the user or pre-computed by the device based on
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