BNMR: PSM (Pol Synth Module)
The PSM/PSM2/PSM3 VME modules are used to produce RF for the bnmr and bnqr respectively. In this document, "PSM" refers to any of these modules. There are significant differences between the modules. The PSM must be run on the bnqr experiment only, and the PSM2 on bnmr only (see #PSM2 for details).
The PSM3 is designed to be run on either bnmr or bnqr. A front-panel switch selects between bnmr or bnqr operating mode. Only one PSM3 module has been built. Currently it is located in the bnmr VME crate and is still being tested.
- Hardware Manuals:
- Programming Guides:
Please refer to the #PSM Manuals from which much of this information is derived.
Status: PSM1 is in use on bnqr.
The POL Synthesizer Module (PSM) is a VME module built at TRIUMF, incorporating a AD9857 Quadrature digital upconverter. It has been designed to generate a complex modulation swept RF signal summed with a reference frequency (fREF). In the case of the PSM, the swept signal may be a single modulated carrier (1f) or include the modulated 3rd and 5th harmonics (3f and 5f). In the case of the PSM2 the 3f and 5f profiles output the same frequency as the 1f profile. They are designed to be used to produce RF shifted in phase compared to the 1f profile by 90 or 270 degrees.
Each carrier is independently modulated.
- the harmonics and the reference frequency ( 1f,3f,5f, fREF) are known as "profiles".
- Do not confuse the "1f" profile with the Experimental (PPG) Mode 1f (Freq) !!
At the time of writing, only the "1f" profile has actually been used in the bnmr and bnqr experiments.
For the bnmr and bnqr experiments only profile "1f" is implemented in the frontend code, except for PPG Mode 1f (Freq) where both profile "1f" and fREF are supported. To avoid confusion, the profile "1f" is referred to in the programs and the custom parameters page as "one-f".
The PSM can be operated in two modes:
- Single Tone Mode
- carrier is not modulated, the output signal consists of a single frequency signal. Frequency data are read from the Frequency Sweep Memory (1f,3f,5f) or from the Frequency tuning register (fREF). At least one strobe must be issued.
- Quadrature Modulation Mode
- both the I and Q data paths are active, the output is a quadrature modulated analog output signal. The I and Q data are read from the I&Q data memory. Each profile (1f,3f,5f,fREF) has its own I&Q memory. If an unmodulated carried is needed, I,Q pairs are set to constant values. When the I,Q memory length is set to zero, the output is modulated by a pair of constant values.
The carriers are synthesized and modulated digitally. In quadrature modulation mode, the modulation data consists of up to 2048 I,Q pairs sampled at a submultiple of the carrier sample rate. The synthesizer circuit interpolates the I,Q sample rate to match the carrier sample rate before modulation.
Status: Deprecated - the PSM3 has now replaced the PSM2 on bnmr.
The PSM is designed for use in the BNQR experiment. The PSM2 module was later designed for use in the BNMR experiment, and is a modified PSM module, running at a higher frequency (up to almost 80MHz compared with the PSM's almost 40MHz). See PSM2 for the differences between the PSM and PSM2.
- Due to a bug in the module, the PSM2 does not support Single Tone Mode. To simulate Single Tone Mode, the PSM2 should be run in Quadrature Modulation Mode with the Idle i,q pair set to (511,0).
Status: PSM3 is in use on bnmr.
The POL Synthesizer Module (PSM3/VFS) is a VME module built at TRIUMF. It has been designed to generate a complex modulation swept RF signal summed with a reference frequency (f1). It comprises four independent frequency channels (f0 Ch1-4) and a fifth reference channel (f1).
The PSM3 has two operating modes (programmable or selected by a switch on the front panel). In BNMR mode, the four frequency channels output RF at the selected frequency in four fixed phases: O,90,180 and 270 degrees output from f0 Ch1-4 respectively. The f1 reference channel outputs the reference frequency at the same phase at the 0 degree channel.
In BNQR mode, the module outputs harmonics of the f0 Ch1 RF on the f0 Ch2-4 channels. In BNQR mode, a phase offset from f0 Ch1 can be programmed for Ch2-4 channels.
The PSM3 has no single tone/quadrature mode register. Single tone mode is achieved by modulating with a fixed I,Q pair of e.g. (512,0).
Idle Frequency, Idle I,Q pair
The PSM defines a location in Frequency memory where a single frequency can be loaded, known as the Idle Frequency location or "Idle". The Idle location is the highest Frequency DM address in the module.
Similarly, in each I,Q pairs memory, the highest address is defined as the Idle I,Q location for that profile/channel.
Loading a frequency value into Idle, resetting the memory pointer to point to this location and issuing a strobe will result in a single RF frequency being loaded, provided...
- the amplitude is set > 0
- external gate(s) supplied or select "gated always"
- PSM/PSM2 :
- the module must not be set to full sleep mode
- PSM :
- select "single tone mode"
- PSM2 :
- load IQ pair (512,0) into Idle I,Q for all enabled profiles
- PSM3 :
- load IQ pair (512,0) into Idle I,Q for all enabled channels
Using the PSM in the BNMR/BNQR experiment
Programming the PSM module (loading the registers/generating frequency/iq files) is done automatically depending on the parameters the experimenter enters on the custom settings page.
The RF calculator program checks the PSM parameters and generates a list of I,Q pairs if needed. This list is stored in the ODB, and read by the frontend, which actually loads the pairs onto the PSM at the start of a run.
The frontend is responsible for computing the frequencies to load. Frequencies can be scanned either within a PPG cycle or outside the cycle. If scanning within a PPG cycle, the full list is loaded onto the PSM memory at the start of the run. If scanning outside the cycle, the new frequency is loaded before each cycle starts.
If scanning within a PPG cycle, a strobe signal from the PPG tells the PSM when to move to the next frequency in the list. If the number of strobes exceeds the number of frequencies, the user can decide whether: the frequency stay sat the final frequency, jumps to the idle frequency, or returns to the first value in the frequency list.
Similarly if an I,Q pairs list is loaded and the gate remains active for longer than the time taken to read out the I,Q memory, the user can decide whether to jump to the idle I,Q pair or the first/last I,Q pair in memory.
In the bnmr and bnqr experiments, the PSM module is programmed differently for a Type 1 (I-MUSR) or Type 2 (TD-MUSR) experiment.