Power supply
Supply the board with +5 V on +Vcc pin and -5 V on -Vcc pin. Do not apply any voltage outside this range on the board.
Warning: Observe the supply polarity. Do not allow the exposed PCB or components to touch conductive surfaces.
Setpoint
Setpoint can be adjusted between -2.5 V and +2.5 V with the SETPOINT trimmer. The setpoint can be modulated with the SETPOINT MOD input. Modulation input is DC coupled, gain is 1 V/V, 0.1 V/V or 0.01 V/V, depending on the MOD GAIN jumper.
Feedback sign
The sign of the feedback for FAST OUT and SLOW OUT can be chosen with the FAST and SLOW jumpers (+1 or -1).
Integrator enable
FAST and SLOW integrators are enabled with the INT EN switch ON. When the switched are OFF, the integrators can still be enabled by applying a voltage between 2.2 V and 4.5 V on the FAST INT EN / SLOW INT EN pins.
Note that when the FAST (or SLOW) integrator is disabled, it behaves as a proportional at low frequencies (see dotted lines in the frequency response graph below). This is intended to facilitate the locking on narrow capture error signals (see https://tf.nist.gov/general/pdf/1819.pdf sec. 1.4.3).
Ramp in
A modulation can be added to the output of the slow integrator SLOW OUT via the RAMP IN pin.
Typical laser-locking setup
In a typical laser lock, FAST OUT drives a fast actuator, such as the CTL200 DC laser-current modulation input. SLOW OUT drives a slower actuator, such as laser temperature control or a piezo. With a PI200-T and CTL200, SLOW OUT can, for example, act through AIN2 for very slow temperature correction.
RAMP IN is added to SLOW OUT and is mainly useful for open-loop scanning of the slow actuator. SETPOINT MOD changes the servo error-signal setpoint instead; it is conceptually different from RAMP IN. Once locked, a scan or ramp is normally not part of the closed-loop operating condition.
In the laser-frequency-stabilization example, the initial scan used to locate the absorption feature is applied externally to the laser controller before the loop is closed. PI200 does not need to perform that initial wide scan.
Input / Output ranges
Input range is ±2 V on the IN and SETPOINT MOD inputs (50 Ω input impedance). Output range is ±2 V in the ERROR, FAST_OUT and SLOW_OUT outputs. ERROR and FAST_OUT have 50 Ω output impedance. SLOW_OUT has 1 kΩ output impedance.
Tuning the frequency response
The frequency response of the loop filter can be adjusted with the 3 blue rotary switches in clockwise order:
PROP: -13.3 dB / -6.6 dB / 0 dB / 6.6 dB / 13.3 dB / 20 dB / 26.6 dB.
FAST INT: 47 kHz / 100 kHz / 220 kHz / 470 kHz / 1 MHz / 2.2 MHz / 4.7 MHz.
SLOW INT (PI200 version): 800 mHz / 2.4 Hz / 8 Hz / 24 Hz / 80 Hz / 240 Hz / 800 Hz.
SLOW INT (PI200-T version): 8 mHz / 24 mHz / 80 mHz / 240 mHz / 800 mHz / 2.40 Hz / 8 Hz.
