LEYSOP M2500 User manual

LEYSOP LTD
Manufacturers and suppliers of optical and electro-optical components
M2500
High Voltage Differential Amplifier
LEYSOP 18 Repton Court, Repton Close, Burntmills, Basildon, Essex, SS13 1LN ENGLAN .
Telephone: 01268 - 522111 Fax: 01268 – 522111 e.mail: [e-mail]

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THIS MUST BE READ BEFORE USING THE
2 00 SERIES AMPLIFIER
2500 SERIES AMPLIFIER
WARNING
THE MAXIMUM OUTPUT UNDER NORMAL CONDITIONS FROM EITHER A OR B
OUTPUT CHANNELS IS 1.5kV. THESE OUTPUTS ARE POTENTIALLY LETHAL
AND EXTREME CARE MUST BE USED IN BOTH USE AND SERVICING OF THE
AMPLIFIER. IT IS ESSENTIAL THAT THE OPERATING INSTRUCTIONS ARE
EXPLICITLY FOLLOWED IN USE, AND SHOULD THERE BE ANY DOUBT ON THE
PART OF THE OPERATOR ABOUT THE USE OF THE AMPLIFIER THE
MANUFACTURERS SHOULD BE CONSULTED.
The amplifier must not be operated out of its case. Only engineers
qualified in high voltage engineering should operate or service this
equipment
IMPORTANT
The amplifier uses SHV output plugs. REMEMBER THAT THEY ARE LIVE AN
POTENTIALLY LETHAL.

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SPECIFICATIONS
AC POWER INPUT 90 – 264 volts AC
50 – 60Hz
SIGNAL INPUT
Input voltage swing for linear operation + 1.25 V
Maximum permissible input voltage + 15 V
OUTPUT VOLTAGES
Normal voltage range for each channel 100 V to 1450 V
Maximum output voltage swing per channel (overdriven) ∼1400 V
Maximum differential output voltage swing (overdriven) ∼2800 V
Maximum differential output voltage swing without clipping ∼2700 V
Output voltage for zero input signal
and zero differential bias setting 750 V each channel
Output voltages for zero input signal one channel 1250 V
and maximum differential bias setting other channel 350 V
Output swing for + 1.0 volt signal input swing +
500 V each Channel
about bias value
Effective differential output swing
for + 1.25 volt input swing 2500 V
Gain (differential output swing) 1000 ( + 2% )
(input swing)
OUTPUT CURRENT
The amplifier is not designed to provide output current into resistive loads.
Capacitive loads will reduce performance.
NOTE
The amplifier has been designed to have a small signal (<500V) frequency response from dc. to
500 kHz. At large signals the frequency response is limited by (1) the slew rate and (2) the
allowable power dissipation. At full amplitude the amplifier can be operated continuously up to
120kHz with a square wave signal and 140kHz with a sine wave at normal room temperatures
(up to ∼ 30°C). Operation above these limits is permissible for limited time but the unit will shut
down when the thermal limit is reached. The “Limited Run Time” LE will light to indicate
that thermal shut down is possible. Operation at high ambient temperature will cause shut down
at lower output drive conditions and possibly without the warning indicator showing.
Continuous operating conditions are shown in the chart on page 8.

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FREQUENCY RESPONSE
Maximum amplitude (2500V differential output) frequency dc to 100 kHz
response before significant distortion
RISE TIME @ Maximum amplitude (2500V differential) <600 nS
@ 2000V differential or less <500 nS
FALL TIME @ Maximum amplitude (2500V differential) <600 nS
@ 2000V differential or less <500 nS
RESPONSE -3dB @ Maximum amplitude (2500V differential) 300kHz
OUTPUT MONITOR
The monitor output is an accurate representation of the differential voltage at the amplifier
output terminals and can be connected to an oscilloscopes 50Ω or high impedance input.
Monitor voltage for 2000V diffential output voltage 1 V into 50Ω load
2V into High Z load
AMPLIFIER FUNCTIONS
Positive limit Variable over 0-100%
of positive differential
output swing V
A
- V
B
Negative limit Variable over 0-100%
of negative diff. output
swing V
B
- V
A
Front Panel differential bias setting Varies differential
output over range + 950V
External C Bias Input +/- 10V C input varies
differential output over range +/-
1000V
Slew rate limit switch. Select as required Off (fastest response)
1 - Rise Time ∼20µS
2 - Rise Time ∼200µS
3 - Rise Time ∼2mS
Output ON switch Turns high voltage outputs on
Output ON indicator Lights when HVoutputs are on
Limited Run Time indicator Lights when thermal shut down
Possible
Over temperature indicator Lights when thermal shut down
has occured

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2500 SERIES AMPLIFIER
OPERATING INSTRUCTIONS
SWITCHING ON
ALWAYS ENSURE THAT THE VENTILATION GRILLS ARE CLEAR OF OBSTRUCTIONS
Switch on the mains switch and note that the AC Power lamp comes on.
NORMAL OPERATION
For normal operation the controls should be set as follows:-
IFFERENTIAL zero
POSITIVE LIMIT 100%
NEGATIVE LIMIT 100%
SLEW RATE LIMIT off
The signal input to the amplifier is connected to the ‘SIGNAL 50Ω’ BNC connector. This presents a 50Ω
load resistance to the signal source which should be suitable to drive this load. The signal input is C
coupled to the amplifier and any offset voltage present will be reflected in the output signals.
A positive transition from zero on the input will cause the A channel output to rise and the B channel
output to reduce and conversely for a negatiove transition. Channel A output, the nett differential output
voltage and the monitor output are in phase with the input while Channel B output is 180 degrees out of
phase with the input.
IFFERENTIAL BIAS CONTROL
The ‘ C BIAS’ control adjusts the mean levels of the A and B output channels.
With the bias control set to zero both A and B channel outputs will be biased to ∼750V.
When the ‘ C BIAS’ control is set to maximum clockwise rotation the A output bias will be ∼1250V,
and the B output bias will be ∼350V. Thus the differential output voltage will be V
A
- V
B
=∼+900V.
When the ‘ C BIAS’ control is set to maximum anticlockwise rotation the A output bias will be ∼350V,
and the B output bias will be ∼1250V. Thus the differential output voltage will be V
A
- V
B
=∼-900V
The ‘ C BIAS’ control allows the output levels to be precisely adjusted across the pockels cells for 'zero
voltage input conditions', thereby achieving the best extinction ratio or lowest residual phase modulation.
Similarly a voltage at the ‘EXT C BIAS’ input will alter the output C bias across the amplifiers
dynamic range. An input of +1V produces a bias of +1000V and -1V produces a bias of -1000V. The ‘ C
BIAS’ control and the ‘EXT C BIAS’ can be used together and the net bias will be the sum of the two
settings.
The digital meter will show the actual C bias voltage at the outputs. (The meter reading will be affected
by low frequency and/or non symmetrical waveforms).

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OPERATION OF LIMITS CONTROLS
The maximum positive differential output voltage V
A
- V
B
, may be precisely limited by the 'positive
limit' control. This is calibrated 0-100% which corresponds to a V
A
- V
B
limit of between 0 and 1500V.
Similarly the 'negative limit' control precisely limits the voltage V
B
- V
A
over the range 0 to 1500V. As
an example, suppose it is required to limit the differential output swing (V
A
- V
B
) to between + 300V
and -900V, the proper settings for the limit controls will be as follows:
'Positive limit' control (300 x 100) = 20%
(1500)
'Negative limit' control (900x 100) = 60%
(1500)
Note that the differential bias control acts 'after the limiting process.
The main use of the limit controls is to provide two precise differential output voltages when the input of
the amplifier is driven from a square wave. This will allow fast switching between two stable precisely
set polarisation states in a pockled cell, or between two levels of optical transmission when the pockled
cell is used between crossed polarisers. The ' ifferential bias' control allows adjustment of the residual
birefringement of the pockel cell, without affecting the limiting polarisation state.
The diagrams of Figs. 1(a), 1(b), 1(c) further illustrate the operation of the limit controls.
Fi 1(a) Shows the A and B output voltage VA and VB and also the differential output voltage (VA-
VB) when both limit controls are set to 100%.
Fi 1(b) Shows VA, VB and (VA - VB) when the limit controls are set to
'POS LIMIT' = 50%
'NEG LIMIT' = 100%
Fi 1(c) Shows VA, VB and (VA-VB) when the limit controls are set to
'POS LIMIT' = 100%
'NEG LIMIT' = 50%
It can be seen in Fig 1(b) that the setting the 'POS LIMIT' control to 50% limits the positive excursion of
VA to 1075V while at the same time limiting the negative excursion of VB to 425V.
Similarly in fig. 1(c) the setting of the 'NEG LIMIT' control to 50% limits the negative excursion of VA
to 425V and the positive excursion of VB to 1075V.
In fig 1(a) the total differential voltage is at the maximum of 2600V while in both Fig 1(b) & 1(c) the
total differential voltage is reduced to 1950V.

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Fi . 1. Showin the effect of limit controls.
+1400V
+100V
+1300V
-1300V
0V
+750V
+425V
+1075V
+650V
-
650V

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SLEW RATE CONTROL
This limits the maximum rate of change of the differential output voltage. The main use of this control
will be to limit the rate of change of voltage across a pockel cell when the input is a square wave of fast
rise time. If the amplifier is to be used for switching an EM500 modulator the maximum slew rate of
2500V/uS may cause mechanical resonance, through piezo-electric effects, and unwanted optical
modulation through the elasto-optic effect.
THERMAL OPERATING CON ITIIONS
This amplifier can be run continuously up to certain limits that are specified by the thermal stress
imposed on internal components. These limits are illustrated by the chart below which shows the safe area
of operation for square and sine wave signals up to ambient temperatures of approximatley 30°C. The
area to the left of the chart lines allows continuous operation where as operating to the right of the line
will light the “LIMITE RUN TIME” LE and will result in the unit turning off to prevent damage.
After shutdown the amplifier will rapidly cool and operation can be restored by moving the “OUTPUT
ON” switch to the off position and switching back ON.
The figures shown on the chart are for guidance only and vary according to ambient temperature, output
voltage, operating frequency, C Offset and waveform. The shutdown system will aways protect the unit
from extreme operating conditions
ue to the high levels of heat generated in this unit there are two fans helping to cool it, one of these is
controlled by the system and when the amplifier is being driven hard this fan will switch to high speed as
conditions dictate. The user will notice an increase in the fan noise under these circumstances. This is
normal.

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Typical Differential Output Waveform at 50kHz and 2500V
Typical Channel A and Channel B Output Waveforms

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Typical rise and fall times at 2500V output
Typical Trian ular Wave at 10kHz and 2500V

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A SIMPLE SETTING UP AND FAMILIARISATION PROCEDURE FOR THE
2500 SERIES AMPLIFIER AND EM500 SERIES MODULATION
Ensure all connections to the amplifier are made correctly and safely.
1. Connect the modulator to the amplifier using the two leads provided.
2. Connect external oscillator to input with 1Hz square wave and amplitude at min.
3. Set Slew rate switch OFF
4. Set positive and negative Output Limits fully clockwise.
5. Switch Output On and increase the input signal amplitude.
6. Check that the amplifier is working by observing the monitor output using an oscilloscope.
7. Hold the modulator between two squares of polaroid with the axis of the polaroid film lying
along the radial axis of the BNC HV sockets and observe a white light source through this
combination. With the polaroids crossed a MALTESE fringe pattern should be seen thus.
As the 1Hz square wave amplitude is increased the Maltese Cross will be changed until at full
amplitude the cross will switch between right hand and left hand output polarisation states as
shown below.
Full +
Output & Sense
Voltage -
There is then a phase shift between the ordinary and extraordinary rays leaving the modulator of
+ 180°. Precise square wave + phase shifting can be achieved between 0 - 180° by adjustment of
the limit potentiometers.
7. If one limit potentiometer is set at zero, only one side of the modulator crystal is driven and the
output polarisation state will switch in one direction only. This arrangement can be used for
amplitude modulation of a laser beam.

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SETTING UP THE MODULATOR WITH A LASER BEAM
The input polarisation must be along the BNC axis or at 90° to that axis.
A suitable output polariser should be crossed to the input polarisation state.
Initially set up the modulator with back reflections along the beam axis. Place a fine ground glass screen
between the input polariser and the modulator and a Maltese cross should be observed after the analiser.
Adjust the modulator position until this cross is central to the beam axis. The best extinction ratio is then
achieved. This must be performed with the EHT switched OFF.
Issue 2.0 4th October 2018