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LCVR Controller Specifications
Nematic liquid crystal driver amplitude and frequency specifications

This liquid crystal controller provides a driver circuit that is compatible with all Liquid Crystal Variable Retarders (LCVRs) and is also ideal for driving most other nematic liquid crystal (LC) devices. This small electronic driver board provides a 2 kHz AC voltage to the LCVR with zero DC bias to prevent polarization and charge migration, which can otherwise limit LCVR device lifetime. The circuit's output frequency is jumper selectable and the drive amplitude is dynamically adjustable with high resolution.

The LCVR Driver Wildcard produces a slew rate limited, 2 kHz, symmetric square wave of programmable amplitude with a precisely controlled 50% duty cycle and zero DC component. The output voltage is programmable, and the frequency may be changed if needed. This LCVR driver may be used with any of Mosaic's microcontroller boards. It requires an analog voltage input, which can conveniently be generated from the DAC output of an Analog I/O Wildcard. The output of the LCVR driver is connected through a coax cable to the liquid crystal device or optical modulator.

The LCVR controller/driver circuit accepts an analog voltage input, Vin, in the range of 0=4.096V and converts it to a square wave magnitude of Vpeak = 2 Vin, or peak-to-peak magnitude of Vp-p = 4 Vin. The square wave's rise and fall times are slew rate limited to 1 μsec (as measured from zero crossing to full amplitude) to minimize overshoot and prevent cable ringing. The circuit's push-pull bipolar transistor output stage quickly charges and discharges cable and LCVR capacitance for fast switching.


LC and LCVR controller schematic diagram

The following block diagram for the LCVR controller depicts the generation of a modulated square wave output from an amplitude-control analog voltage input:

Liquid crystal variable retarder (LCVR) controller schematic
Fig. 1  Schematic block diagram of the OEM electronic controller board for liquid crystal variable retarders (LCVR) with selectable frequency and programmable amplitude.

The circuit's analog voltage input (generally taken from a DAC output of an Analog I/O Wildcard) is amplified and modulated to produce a square wave with a nominal frequency of approximately 2 kHz. The frequency is jumper selectable at appx. 1 KHz, 2 KHz or 4 KHz1), or an external logic-level frequency input may be used.


LC controller electrical and physical specifications

Physical Specifications
Weight 20 gram
Footprint Wildcard size, 2" × 2.5" × 0.415"2)
Power requirements 5 VDC at 1 mA and 13.5 to 26 VDC at 12 mA from PDQ V+RAW, or,
5 VDC at 1 mA and 10.7 to 12.5 VDC at 12 mA from PDQ V+RAW (by installing R21)
Operating temperature 0 to 50°C
Humidity 5 - 95% RH noncondensing
Input characteristics
Control Voltage 0–2.048 or 0–4.096 V full scale (FS) from an Analog I/O Wildcard or other programmable voltage source
Control Voltage
Input Impedance
6 kΩ
Input Clock If an external clock is supplied its logic levels must be:
Input logic high: 3.5 to 5.0 V
Input logic low: 0.0 to 1.0 V
Output characteristics
Output form Square wave with zero DC component
Output impedance 5 Ω
Frequency Default 1953.125 Hz, resistor selectable to 3906.25 or 976.5625 Hz, or externally driven
Frequency stability ±100 ppm (-10°C to +70°C) ±5 ppm/year when using a 16 MHz clock from a Mosaic controller
Duty cycle 50% ± several ppm measured from zero crossings
Amplitude and resolution Vp = 0 to ± 4.096 V FS in 0.001 V steps, or
0 to ± 8.192 V FS in 0.002 V steps
Maximum average
output current
±30 mA
Rise/fall times Slew rate limited, 1 μsec max from zero crossing
Slew rate Limited to 8 V/μsec
DC offset < 5 mV max (typically < 1 mV)
< 1 mV when disabled
Overshoot < 0.5 V (1st peak), < 3 μsec ring-down (< 1.5 typ.) for Vp =1 V, times measured from zero crossings
Maximum load capacitance 100 nF
LCVR connector PCB mounted, male contact, vertical RP-SMB jack 3)

There are a few subtleties of the circuit's specifications:

  • The DC offset is typically less than 1 mV for voltages up to Vpeak = 5 V. For greater voltages, there is a slight asymmetry of the output waveform's rise and fall times accounting for an effective DC offset of at most ±Vpeak/1000. The output is DC coupled.
  • The gain of the board is precisely 2, so that Vpeak = 2 Vin. The voltage accuracy of the output magnitude is determined solely and entirely by the accuracy of the input voltage, which would normally be taken from a DAC output of an Analog I/O Wildcard.

Using the LCVR controller in an OEM scientific instrument

There are several analytical instruments that benefit greatly when using LCVRs or other inexpensive electrically switchable retardation plates. In particular, LCVRs allow producing inexpensive polarimeters, for high-precision spectropolarimetric measurements at very low cost. They are also used for fluorescence microscopy. In that case, a polarizer and a quarter-wave plate combined with a liquid crystal variable retarder allows tuning or rotating the angle of polarization of light prior to its illuminating a specimen in a fluorescence microscope.

For detailed instructions on installing, connecting to, and using this electronic controller for LCVRs, see the LCVR Controller User Guide.

Actually, multiples of 1953.125 Hz, which are derived from a 16 MHz signal on the Wildcard bus
Height is from the bottom of the PCB to the top of the tallest component on the top side of the PCB. Additional space may be required for attaching an SMB cable. Additionally, connectors protrude from the board's bottom side by 0.340".
This RP-SMB recepticle is equivalent to standard reverse-polarity SMB sockets such as Amp/Tyco PN 5221111-1 or Digikey PN A99875-ND and accepts right angle, reverse polarity RP-SMB plugs and cables such as Emerson cable 415-0001-036 (Digikey PN J1036-ND)
This page is about: Liquid Crystal Variable Retarder (LCVR) Controller Specifications – Electronic controller/driver board for Liquid Crystal Variable Retarders (LCVRs) and other nematic liquid crystal devices. Its 2 kHz AC square wave has zero DC bias to prevent charge migration or electrode polarization of the LC, which can otherwise limit LCVR lifetime. Drive frequency is jumper selectable and voltage amplitude is dynamically adjustable with high resolution. liquid crystal tunable filter, optical phase modulator