Download Documentation for GAIN setup

Documentation for GAIN setup
Basic theory
Gain calculation of avalanche photodiodes (hereafter referred as ‘apds’) is done by
measuring the output current of the apd while applying different bias to it and dividing
the difference from light current to dark current by the difference at gain one (usually at
<30V).
(Note: For the operation of the setup please refer to the lab manual for the setup)
Description of the Gain setup
The heart of the gain setup is the aluminum box which houses the light distribution fibers
mounted on the aluminum base plate which is through holed for water chilling and fits
the circuit housing 20 apds on its base so that the apds are very close to the aluminum for
air contact chilling. This whole apparatus is covered with a thermal shield of aluminum,
foam and aluminum in that order to ensure thermal stability irrespective of room
temperatures. Chilling for the setup is provided by Neslab RTE-111D chiller through the
two tubes for the water flow. A AD590 temperature sensor mounted very close to the
apds monitors the setup temperature.
APDs are mounted on the 20 channel circuit in the ZIF sockets and can be screwed to the
base of the aluminum plate. Voltage is applied to each individual apd one by one while
the others are not under bias so as to reduce leakage currents. Keithley 7001 switch
system with two Keithley 7154 HV switching cards are used to switch the apds. The
currents are precisely read by the Keithley 487 and it also provides the bias for the apds.
The light output is monitored in conjunction by a PIN diode using a Keithley 485.
The labview program takes data and calculates the gain, dM/dV and stores it in an ASCII
text file on the local machine and also in the cristal database.
Calculation of Gain, dM/dV and dM/dT
For Gain 1 calculation four readings starting from the index 3 of the voltage array. For
example if the first stop at V is 60 with a 5 V step width the mean will be of values at 25,
30, 35 and 40V, since in this case of the settings in the front panel diagram the start at V
value is 10V, therefore index 0 is 10V index 1 is 15V and so on till index 3 to 6 are 25 to
40V. The gain equation used is (Itotal-Idark)/Mean of the 4 values(Itotal-Idark). The gain
at 50 is found by interpolation among the closest set of values for gain.
dM/dV is measured by dM/dV * 1/M = (Mn - Mn-1)/(Vn - Vn-1)/(Mn+Mn-1) * 200
where M is the Gain and V the bias.
dM/dT is not calculated by the program and needs to be separately done since the
program was initially designed for only single temperature. The equation to be used is
1/M(dM/dT) = -100/(Avg M for the two temperatures)*((M at temp 1- M at temp 2)/2)
Detailed description of the settings and instrumentation
Data Acquisition with National Instruments AT-MIO-16XE and BNC-2090
National Instruments AT-MIO-16XE card is used in with a BNC-2090 adapter to bias
three 470nm Nichia LEDs that supply the light. The typical light currents read by
hamamatsu apds at ~25C with respect to the bias are as follows:
LED Bias
APD Current (G=1) APD Current (G=50)
PIN Current
2.72V
25-35nA
500-800nA
50-75nA
2.92V
30-40nA
1-2A
75-85nA
Also the temperature sensor is monitored by the BNC-2090. The PIN photodiode is
biased by the BNC-2090. Settings currently used on the BNC-2090 with the Gain setup
are as follows.
ACH0  Temperature Sensor Analog Input (10V range, Single ended, SE setting on
the BNC-2090 adapter)
DAC0OUT  LED Bias Analog Output (-2.92V or , RSE setting)
DAC1OUT  PIN Bias Analog Output (~5V or , RSE setting)
Test panel for the BNC-2090 can be found from StartProgramsNational Instruments
DAQNI-DAQ Test Panels or from the Devices and instruments option in the
measurement and automation explorer.
There are no configurable hardware settings on the AT-MIO-16XE DAQ card. Software
settings are generally automatic with Windows NT but in case of problems one can
reassign them from the control paneldevices by trying to uninstall and reinstall.
GPIB (IEEE 488.2) card National Instruments AT-GPIB/TNT
Current settings for the switch are as in the table below, these correspond to the software
hex address of 0x2c0 for the card. Also the DMA is set to 5 for which the DRQ5 and
DACK5 are jumpered. And Interrupt level 10 is selected by jumpering IRQ10.
A9
OFF
A8
ON
A7
OFF
A6
OFF
A5
ON
Note: The picture below is just to show the position of the switches on the GPIB board
and an example of the settings, but the current settings on the board inside pcminn01 are
as mentioned above.
For more info on setting the GPIB settings refer the GPIB manual from National
instruments.
Neslab Chiller RTE-111D settings and control
The chiller needs to be in the remote mode for computer control. Settings can be changed
by the front panel buttons as described in the manual. The RS-232 port on the back of the
digital controller is connected to the COM1 port of the PC with a normal RS-232 male to
female cable.
Serial port software settings for the chiller are :
9600 baud, 1 start bit, 8 data bits, 1 stop bit and no parity.
Also the chiller only understands ascii hex characters. Use the labview vi set_temp.vi to
play with the chiller temperature.
The chiller needs about 2 liters of distilled water to fill and needs to be refurbished about
every 36 hours or more of operation.
Note: To chill below 8C (-25C to 8C) use a 50/50 mixture, by volume, of distilled water
and laboratory grade ethylene glycol.
Keithley 487 settings
The device currently being used with the setup already has all the device settings saved as
the default power ON settings. If needed to restore choose
Line frequency
Current limit 
Trigger Interval
Trigger Source 
GPIB address 
50Hz for Switzerland,
2.5mA
0.3s
External
23
Connections to the backplane of 487:
Current to be measured  INPUT using a 3lug TriaxBNC connector
Voltage to be supplied  V-Source Output using BananaBNC connector
GPIB connection via a GPIB cable to the computer GPIB port or any bus using the same
GPIB card.
Keithley 7001 Switch system and Keithley 7154 HV switching card settings
The 7001 is a pretty easily configurable device. Choose cards 7154 for each slots via the
front panel card configuration and the GPIB address to 07 and the rest is factory default.
The 7154 HV switching cards are screw terminal cards where the connections for the apd
bias and the current (i.e connections to both legs of apds, 2 per apd) are wired
permanently. The current wiring of the cards in use with the gain setup has the following
switch selections on the front panel when used with the new apd circuit with the line ZIF
sockets.
NOTE: Please carefully mount the APDs in the ZIF socket using only the PINs as shown
above (1,3 5,7 13,15 17,19). If not mounted correctly the apd connections being wrong,
results into junk data.
From the circuit with the apds a ribbon cable connects to the screw terminals of the 7154
cards. HHigh Voltage leg of the apd (i.e the cathode) and LCurrent sensing leg of
the apd. Since the G for all terminals are internally connected one need only connect any
one of the GGround of the circuit.
The output terminals of the 7154 cards are connected to two denuded BNC cables in the
following fashion: GG and connect the junction to the G on board the 7154 output
terminal. One BNC main is connected to H and the other to L. The two H BNCs are then
taken out of the system and connected in a T and further connected to the Keithley 487
V-source output. And the two L BNCs are connected in a similar fashion via a T to the
Keithley 487 Input using the TriaxBNC adapter.
Keithley 485 and PIN monitoring
Set the GPIB address to 22 and push the AutoRange button on the front panel if not
already selected. GPIB address can be configured via the hardware switch on the back.
Connect the input on the front panel to the appropriate lemo connector on the circuit as
shown below. Also the GPIB slot at the back should be connected to the GPIB bus or the
GPIB card in the computer.
Temperature Sensor Analog Devices AD590 and PIN diode EG&G
VTB8441B monitoring and settings
The temperature sensor is mounted in the middle hole in the aluminum base plate and
connections are drawn through the ribbon cable that connects on board the circuit with
the 8 pin connector as shown in the figure above. The connections of the ribbon cable are
described below.
PIN 1  AD590 +ve
PIN 3  AD590 sense
PIN 4  PIN diode (VTB8441B) sense
PIN 8  PIN diode (VTB8441B) +ve
Calibration is needed for the AD590 it is important to ensure utmost temperature
precision. Temperature sensing is done via the DAQ card using Analog Input channel
ACH0 on the BNC-2090. It reads a voltage across a 10K resistor in series with the sense
pin of the AD590. PIN current is measured precisely by the Keithley 485 and fed into the
computer via GPIB.
SOFTWARE DESCRIPTION
Program location: On PC pcminn01 D:\Projects\APDs\apd_TEST_V3.vi
Program Library: On PC pcminn01 D:\Projects\APDs\apd_TEST_V3.llb
The program apd_TEST_V3.vi is the current version used to measure all apds for gain.
It measures gain for 20 apds automatically and saves data in ascii text files on the local
hard drive and also the cristal database.
Typical settings on the front panel can be seen in the figure below. With these settings
when the program is run first it will set the chiller to the temperature entered in Chiller
Temp and waits till the temperature reading from the AD590 inside the setup is ±0.5C.
Once the temperature is reached the program sets the Keithley 7001 switch to close the
first position 1!1. The next step Initializes the Keithley 487 to the range for Light ON
since the light curve is done first. Light is now turned ON by applying bias to the LED
(currently –2.92V) and there is a waiting of 90 seconds to stabilize the light from the
LED. After this the voltages from the voltage array are scanned and at each point the
Current from the apd, current from PIN diode and the temperature from AD590 are
plotted on the front panel. Once the light curve data is taken light is switched OFF by
turning the LED bias to 0V, and a similar dark curve is taken. At the end the breakdown
voltage for the apd is calculated by increasing the bias from the last point measured in
steps of 0.1V till the current reaches 100µA.
Gain, dM/dV are calculated and stored along with other parameters in a file
G0301900001.txt at the location: D:\APD_DATA\New_apds\Lot_3_Wafer_1\25C
In the directory specified (here D:\APD_DATA\New_apds\) the program creates a folder
Lot_3_Wafer_1 and in this folder creates a folder 25C (and 18C when the program is run
for 18C or similarly for any temperature) and stores the text file named G0301900001.txt.
Apd_TEST_V3.vi Front Panel
Note: For more instructions on operation please refer to the Lab Manual for the Gain
setup.
A typical data output file from the above settings:
APD#;900003;LotNumber;WaferNumber;3;1;Date/Time;4/5/2000;9:30:57
PM;FileLocation;d:\Apd_data\New_apds\Lot_3_Wafer_1\25C\G0301900003.txt;
Vr;Idark;dM/dV;MeanTemp;Vb;QEcoefficient;APDPosition;APDNumber;
350.56;10.39;3.21;25.00;395.70;0.5630;3;0301900003;
Voltage;Itotal;Idark;Iphoto;Gain;dM/dV;Idark/Gain;Gain_dM/dV;Ipinlight;Ipindark;AP
DStatus;new;
10.000;37.900;-0.800;38.700;1.001;-0.052;-0.799;0.999;68.700;0.000
15.000;37.900;-0.700;38.600;0.998;0.052;-0.701;0.999;68.690;0.000
20.000;38.000;-0.700;38.700;1.001;-0.052;-0.700;0.999;68.690;0.001
25.000;38.000;-0.600;38.600;0.998;0.052;-0.601;0.999;68.710;0.000
30.000;38.100;-0.600;38.700;1.001;0.000;-0.600;1.001;68.710;0.001
35.000;38.100;-0.600;38.700;1.001;0.000;-0.600;1.001;68.720;0.001
40.000;38.200;-0.500;38.700;1.001;0.000;-0.500;1.001;68.740;0.001
45.000;38.200;-0.500;38.700;1.001;-0.052;-0.500;0.999;68.720;0.001
50.000;38.200;-0.400;38.600;0.998;0.052;-0.401;0.999;68.730;0.001
55.000;38.300;-0.400;38.700;1.001;0.000;-0.400;1.001;68.750;0.001
60.000;38.300;-0.400;38.700;1.001;0.102;-0.400;1.027;68.750;0.001
110.000;40.767;0.033;40.733;1.053;0.550;0.032;1.221;68.730;0.001
160.000;54.067;0.333;53.733;1.389;1.278;0.240;2.041;68.800;0.001
210.000;105.133;0.967;104.167;2.693;1.596;0.359;4.481;68.780;0.000
260.000;244.533;2.067;242.467;6.269;1.862;0.330;11.732;68.780;0.000
310.000;669.500;4.500;665.000;17.195;2.283;0.262;18.235;68.780;0.001
315.000;750.200;4.700;745.500;19.276;2.348;0.244;20.478;68.790;0.000
320.000;843.600;5.100;838.500;21.681;2.433;0.235;23.085;68.790;0.001
325.000;952.800;5.700;947.100;24.489;2.521;0.233;26.136;68.800;0.001
330.000;1080.833;6.300;1074.533;27.784;2.622;0.227;29.733;68.810;0.000
335.000;1232.300;7.000;1225.300;31.682;2.748;0.221;34.019;68.790;0.001
340.000;1414.000;7.900;1406.100;36.357;2.901;0.217;39.200;68.800;0.001
345.000;1634.900;8.900;1626.000;42.043;3.077;0.212;45.546;68.840;0.001
350.000;1907.200;10.200;1897.000;49.050;3.261;0.208;51.573;68.810;0.001
353.000;2103.333;11.200;2092.133;54.095;3.414;0.207;57.015;68.820;0.001
356.000;2330.300;12.300;2318.000;59.935;3.596;0.205;63.352;68.810;0.001
359.000;2595.800;13.500;2582.300;66.769;3.819;0.202;70.826;68.820;0.000
362.000;2911.100;15.000;2896.100;74.883;4.079;0.200;79.763;68.820;0.000
365.000;3290.300;16.700;3273.600;84.644;4.397;0.197;90.621;68.830;0.001
368.000;3754.800;18.900;3735.900;96.597;4.806;0.196;104.101;68.860;0.001
371.000;4337.833;21.500;4316.333;111.605;5.307;0.193;121.258;68.840;0.000
374.000;5087.900;24.933;5062.967;130.911;5.951;0.190;143.741;68.850;0.000
377.000;6084.933;29.500;6055.433;156.572;6.851;0.188;174.506;68.860;0.001
380.000;7478.300;35.700;7442.600;192.440;8.138;0.186;219.198;68.850;0.000
383.000;9557.434;45.100;9512.333;245.956;10.119;0.183;289.967;68.850;0.000
386.000;12977.134;60.533;12916.600;333.978;13.527;0.181;418.993;68.860;0.001
389.000;19583.268;90.767;19492.500;504.008;0.000;0.180;0.000;68.880;0.001
Troubleshooting for Gain setup
Problem
Possible Reasons and Solutions
1. No good data (gain curve looks random)
Check that apds are connected right, i.e
right slots and the IDC ribbon connector is
connected. And with light ON try to read
the apd current from the keithley 487.
Check the water level and add water to
maintain water near high in the bath.
This happens when there is already an
existing file with the same name. Save in a
different directory.
Make sure the database file being written is
not accessed from any other pc or is not too
big. (>750kb) if so use a new file to store
the database.
Make sure the LED lemo is connected to
the DAC0OUT on the BNC-2090
Possibly the current limit is exceeded.
Make sure you are in the right range for
expected currents for light ON and light
OFF. Normally set to 20A
2. Chiller makes too much noise
3. Program stops at every apd for user
intervention to replace existing file
4. Program stops saying error writing file,
continue or stop
5. No light, PIN diode reads 0 even with
light ON
6. The program doesn’t scan voltages till
the end of the voltage table, stops
somewhere before the last setting.
Location of this document: On 'pcminn02'
E:\Documentation of setups\Documentation for gain setup.doc
CIRCUIT DIAGRAM FOR PCB USED IN GAIN SETUP
Location of PCB files (binary) for this circuit on pcephc51
D:\Final circuits made by bpatel\Apd_new_1.pcb
Hamamatsu APD Drawing showing the connection description for anode/cathode.