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2612B End of Pulse Configuration

Models 2601, 2602, 2611, 2612, 2635, 2636
Models 2601A, 2602A, 2611A, 2612A, 2635A, 2636A
Models 2601B, 2602B, 2604B, 2611B, 2612B, 2614B, 2634B, 2635B, 2636B
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Posts: 93
Joined: September 23rd, 2014, 6:14 am
Country: United States

2612B End of Pulse Configuration

Post by jaime_g » March 7th, 2017, 4:48 pm

I have been trying configure an SMU 2612B so the end of a 15ms, 10mA pulse applied to a photo diode reaches 0V at the end of the pulse width.
However, the falling edge of the pulse will not reach 0V. Instead, for 600µs the pulse hangs at about 0.2V then drops to -0.1V for another 600µs before reaching 0V. The pulse level hanging at 0.2V affects the turn off time measurement of a Solid State Relay, which is a power MOSFET.

Here is the oscilloscope trace:
TDS3052C Trace_53259 Turn On Delay.jpg
TDS3052C Trace_53259 Turn On Delay.jpg (1.96 MiB) Viewed 10058 times
Here is the SMU2612B code that generates the pulse:

Code: Select all

smua.sense = smua.SENSE_REMOTE
smub.sense = smub.SENSE_REMOTE

--Configure smua source
smua.source.func = smua.OUTPUT_DCAMPS
smua.source.autorangei = smua.AUTORANGE_OFF
smua.source.rangei = 10e-3
smua.source.leveli = 0
smua.source.limitv = 0.02

--Configure smub source
smub.source.func = smub.OUTPUT_DCVOLTS
smub.source.autorangev = smub.AUTORANGE_OFF
smub.source.rangev = 200
smub.source.levelv = 50
smub.source.limiti = 25e-3

--Configure smua trigger count
smua.trigger.arm.count = 1
smua.trigger.count = 1
smua.trigger.arm.stimulus = 0

--Configure smua pulse width timer
trigger.timer[1].delay = 15e-3
trigger.timer[1].count = 1
trigger.timer[1].passthrough = false
trigger.timer[1].stimulus = smua.trigger.ARMED_EVENT_ID

--Configure smua source action
smua.trigger.source.limitv = 1.9
smua.trigger.source.action = smua.ENABLE
smua.trigger.source.stimulus = 0

--Configure smua measurement action
smua.trigger.measure.action = smua.DISABLE

--Configure smua end of pulse action
smua.trigger.endpulse.stimulus = trigger.timer[1].EVENT_ID
smua.trigger.endpulse.action = smua.SOURCE_IDLE

smub.source.output = smub.OUTPUT_ON
smua.source.output = smua.OUTPUT_ON
smua.source.output = smua.OUTPUT_OFF
smub.source.output = smub.OUTPUT_OFF
I notice that programming smua.source.limitv = 0 will not generate a pulse.

Any help in resolving this issue will be appreciate it.

Jaime Arevalo

Andrea C
Keithley Applications
Keithley Applications
Posts: 1436
Joined: October 15th, 2010, 10:35 am
Country: United States

Re: 2612B End of Pulse Configuration

Post by Andrea C » March 13th, 2017, 5:34 am

Hi Jamie,

Your diode has junction capacitance. When you pulse current and resume 0Amps at end of pulse, you can easily trap charge on the capacitance and a voltage potential will be the result.
I suspect the transition to negative voltage is due to the smu output being switched off (blue light) and with normal output off state in force, the SMU is forcing 0V with ability to source or sink current in order to maintain 0V.

I also want to note two settings:
smua.source.limitv = 0.02

smua.trigger.source.limitv = 1.9

The trigger source limitv applies only during your 15msec pulse.
When end pulse event occurs, trigger model returns to idle state and the value set by "smua.source.limitv" applies. If the voltage potential on the diode due to trapped charge is larger than this idle state limit, you could be driving the SMU into voltage compliance (clamping). You could be having some additional interesting artifacts due to this. As simple test, try raising the value from your 20mV value. Does the ~200mV level on your scope increase in value?

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