The 50mA Source Measure Unit is a highly specialized and precise instrument tailored for testing and characterizing low current light emitting devices, such as VCSEL singlets, single emitters, micro-devices, and nanofin LEDs. The ability to provide both DC current and precision pulsed current with excellent pulse fidelity at low currents is crucial for accurately assessing the performance and characteristics of these devices.
Key Features
- Pulse width range: 10 μs minimum to 15000 s
- Max DC output power: 5 W
- Max pulsed output power: 5 W
- Clean pulse shapes
- Minimal distortion
- High repeatability
Applications
Pulse Scope Shot
Pulse scope shots demonstrate the stability and accuracy of delivered current under demanding conditions. You can rely on these waveforms to verify that every pulse remains free of distortion, overshoot, or unwanted noise, ensuring repeatable and trustworthy test results.
LIV Curves
LIV curves provide a complete view of device performance by combining light output, current, and voltage into a single, time-aligned measurement. Using precision pulsed SMU technology, engineers can accurately characterize efficiency, threshold behavior, and overall device performance with minimal thermal distortion.
Spectral Response
A spectral response test using a Vektrex Source Measure Unit characterizes how a device responds electrically across different wavelengths of light, from ultraviolet through infrared. By precisely biasing the device and measuring its current or voltage response at each wavelength, the system generates a detailed spectral response curve that reveals sensitivity, peak performance, and cutoff regions. This capability is essential for evaluating photodiodes, image sensors, solar cells, and other optoelectronic devices where accurate light-to-electrical conversion performance is critical.
50mA Source Measure Unit Specifications
| PSMU-PRF Specifications | 50 mA (Max Current) |
|---|---|
| Overall | |
| Min Output Voltage | 0 V |
| Max Compliance Voltage | 50 V, 100 V, 200 V, 400 V |
| Source Channels | 1 |
| Max DC Output Power | 5 W |
| Max Pulsed Out Power4 | 5 W |
| Pulsing | |
| Pulse Width Range12 | 10 μs minimum to 15000 s |
| Pulse Width Resolution10 | 0.1μs (11 ns w/ Pulse Width Offset10) |
| Pulse Width Accuracy2,10 | 1μs (50 ns w/ Pulse Width Offset10) |
| Pulse Rise/Fall Time3 | 200 ns – 3 μs |
| Typical Pulse Width Jitter | 30 ns |
| Timebase Accuracy | 50 ppm |
| Pulse Period Range13 | 11μs – 30000 s, depending on model |
| Duty Cycle Range | Programmable 0-100%, no current limits, limited by Toffmin of 20 μs or 9 μs (1μs model) |
| Pulse Count | 0 – 12000000 (Multiple Pulse and Pulsed Sweep modes) |
| Sweep Steps | 3 – 10000 (Pulsed Sweep mode) |
| Low Range Current | |
| Max Current | 4 mA |
| Setpoint Resolution | 100 nA |
| Output Current Accuracy | 0.05% + 6 μA |
| Min Recommended Current | 6 μA |
| High Range Current | |
| Max Current | 50 mA |
| Setpoint Resolution | 1 μA |
| Output Current Accuracy | 0.05% + 10 μA |
50mA Source Measure Unit Specifications Continued
| PSMU-PRF Specifications | 50 mA (Max Current) |
|---|---|
| Miscellaneous | |
| Nominal Current Ripple1 | <1mA: 4 μA 1 mA to 10 mA: 40 μA 10 mA to 50 mA: 17 0μA |
| DC Ramp Rate: Low Speed Setting | 10 V/s, 50 mA/s |
| DC Ramp Rate: Default Setting | 10 V/s, 500 mA/s |
| DC Ramp Rate: High Speed Setting | 1000 V/s, 50 A/s |
| Current Stability9 | 70 ppm |
| SpikeSafe Transient Protection | Power shutdown timing ns. (voltage monitor accuracy: 3% +1 V | current monitor accuracy: model dependent) |
| Bias Current5 | |
| Max Current | 33 mA |
| Setpoint Resolution | 1 μA |
| Bias Current Accuracy | 0.35% + 60 μA |
| Fall Time to Bias Current | 200 ns – 3 μs |
| 5% Settling Time After Falling Edge7 | 10 – 70 μs |
| 0.1% Settling Time After Falling Edge8 | 70 – 130 μs |
| Modulated Current6 | |
| Sequence Step Amplitude Range | 0-100% |
| Min Step Width | 1 ms |
| Max Step Width | 10 s |
| Step Width Accuracy | 10 μs |
| Max Number of Steps | 20 |
| Max Number of Steps (Loops) | 3 |
| Loop Count | 1 to 32767 or Infinite |
| Current Rise/Fall Time Each Step3 | 5 – 8 μs |
General SpikeSafe SMU Specifications
| Current Out | |
| Digitizer Channels | 1,2 |
| Output Current Drive Type | Floating, both + and – terminal driven, max 100 V common mode to chassis ground |
| Output Cabling | Single or multi-conductor twisted pair |
| Recommended Max Output Cable Length | 6 m |
| Trigger In | |
| Signal Type | 5 V logic, VIH > 3.5 V, VIL < 1.5 V |
| Polarity | Programmable |
| Modes Supported | Multiple Pulse, Pulsed Sweep, Modulated Current |
| Programmable Delay | Programmable delay, 10 μs to 30 s |
| Delay Programming Resolution | 1 μs |
| Delay Jitter | Multiple Pulse Mode: 3.4 μs, Pulsed Sweep Mode: 107 μs |
| Trigger Out | |
| Signal Type | 5 V logic, 50 Ω pull-up and open drain outputs |
| Polarity | Programmable |
| Modes Supported | All pulsed modes, Software trigger in DC mode |
| Trigger Jitter | <10 ns typical |
| Programmable Delay | Programmable delay, 10 μs to 30 s |
| Other External Factors | |
| General Purpose Input (EXT_GPI) | Optoisolated input, generates External Pause SYST:ERR? Event, VLow Max: 0.75 V, VHigh Min: 2.72 V, VHigh Max: 27.2 V |
| Remote Disable (Interlock) | Optoisolated input, halts output, selectable polarity, VLow Max: 0.75 V, VHigh Min: 2.72 V, VHigh Max: 27.2 V |
| General | |
| Physical | Rack mount/bench top chassis 1/2 Rack 89 mmH x 213 mmW x 452 mmD Weight: 8 lbs, 3.6 kg |
| Input Power | AC 100-240 VAC, 700 W, Single Phase |
| Remote Control | 100-base T Ethernet, TCP/IP with SCPI syntax |
| Monitoring System | Built-in acquisition system monitors & reports voltage, current, and fault conditions |
| Device Protection | 3rd generation SpikeSafe protection including high-speed over current shutdown, slow start up, leakage detection and other protection algorithms |
| Calibration Interval | 1 year calibration interval recommended |
| Operating Conditions | For indoor use only, 10 C to 35 C, <2000 m altitude |
| Cooling | Air cooled |
| Particulate Level | Clean lab conditions |
| Other | CE, ROHS, ISO17025 certification |
Operating Modes
| Operating Mode | Description | Typical Application |
|---|---|---|
| Bias | Constant DC bias current – generally used for SVF (voltage sensitivity factor) determination. | Thermal Resistance and Tj measurements. Bias may be added to many operating modes. Requires purchase of optional BIAS. |
| Continuous Dynamic | Continuous pulse train – current changes may occur while the source channel is enabled. | PWM, production binning, closed-loop power control. |
| Continuous Pulse | Continuous current pulse train that transitions on and off according to configured pulse parameters. | Continuous pulse light measurements to reduce junction heating. Any other continuous pulse application. |
| CW Sweep | Constant wave current sweep. | Typical characterization test where output parameters like power are monitored over a range of input power levels. |
| DC | Direct current. Also known as constant current or constant wave. DC dynamic mode allows current to be changed +/- during DC operation. | Any constant current application. LM-85, light measurement, characterization, R&D, production. |
| DC Dynamic | Constant current – current changes may occur while the source channel is enabled. | Low speed > 10s pulsing. Software controlled pulsing. Useful for TEC control. |
| Modulated Current | A programmable sequence of DC current steps that define a waveform. Sequences may be finite or run indefinitely. | Cell phone flash emulation, rectifier ripple emulation. Requires purchase of optional Modulated Current function. |
| Multiple Pulse | Similar to Single Pulse mode, but allows a programmable number of pulses to be output. | Fixed pulse count device testing. Also recommended for Single Pulse use (1 pulse). |
| Multiple Pulse Burst | Multiple bursts of pulses with defined pulse and burst timing, and current changes. | Burst L-I-V sweeps, high duty cycle sweeps. |
| Pulsed Sweep | Also known as QCW (quasi-constant wave). Primarily used to minimize self-heating such as with I-V, L-I, and LIV curves. Pulsed sweep on/off may be used to thermally stress devices or speed lifetime test. Also used for withstand or limit testing. Step number reported at error used to identify failure current. | I-V plots for LEDs, lasers, and other semiconductors. L-I plots for optoelectronics, overcurrent protection circuit tests, pulse withstand testing. |
| Repetitive Burst Mode | Multiple bursts of bursts. | VCSEL testing. Customer specific applications. |
| Single Pulse | Also known as mono pulse. One pulse output (one transition on and off) according to configured pulse parameters. | Any single pulse application. LM-85, light measurement, characterization, R&D, production. |
Digitizer Specifications
| Digitizer Channels | 1,2 |
| Measure Method | 4 wire |
| Ranges | 3 Ranges, 10 V, 100 V and 400 V |
| Input Impedance | 1 MΩ -1.4 MΩ |
| Disconnect Relay | Disconnect Sense +/- terminals when Digitizer is placed in 0 V range |
| Coupling | DC Coupled, All Ranges |
| Maximum Common Mode | Sense+ or Sense- must be <420 VDC from Chassis Ground or Force+ or Force- |
| ADC Sample Rate | 500,000 samples/second, continous sampling |
| Digitizer Type | True differential |
| Resolution | 18 Bits |
| Programmable Measurement Aperture | 2 μs to 400 ms, 500 kHz samples boxcar averaged to form measurement points |
| Measurement Trigger | Software or hardware |
| Hardware Trigger Edge Polarity | Programmable |
| Trigger Delay | Programmable 0 to 400 ms, 2 μs resolution |
| Measurement Points Per Acquisition | 1 to 525 |
| Autozero Function | Reduces measurement offset |
| Sampling Method | Logarithmic sampling to 1000 s, and custom programmable sampling available with +BIAS option |
Digitizer Range Specifications
| Ranges | 10 V | 100 V | 400 V |
|---|---|---|---|
| Maximum Voltage | 10.4 V | 112.2 V | 420.6 V |
| Typical Noise, RMS14 | 100 μV | 200 μV | 500 μV |
| Input Impedance | 570 kHz | 290 kHz | 570 kHz |
| Accuracy | 0.03% + 300 μV | 0.09% + 3 mV | 0.06% + 30 mV |
Force Sense Selector Switch Specifications11
| A/B Function | Used to route external auxiliary device to the Force and Sense output terminals. Allows SMU and auxiliary instrument to share load wiring. |
| Connect/Disconnect Function | Rapid connect/disconnect of load to protect probe points. Eliminates time to disable/enable power speeding production. |
| Control | One SCPI command, programmable power-on default, switching time < 1 ms |
| Guarded | Yes |
Footnotes
| All source specifications at 23 C+/-5 C, pulsing specifications: outside cable <3 m. |
| All digitizer specifications at 23 C+/-5 C, 5% to 80% relative humidity, noncondensing after autozero and a 90 minute warmup period. |
| 1 RMS, 20 MHz BW, primary frequency 100 kHz or 200 kHz. |
| 2 Typical performance with automatic adjustments enabled, compensation settings tuned for best shape, I > 10% Imax, Pulse Width <10 s. |
| 3 Typical performance with compensation settings tuned for fastest rise and best pulse shape, I > 10% Imax. |
| 4 Typical energy per pulse available: 1.5 J |
| 5 Requires BIAS option. |
| 6 Requires MODI option. |
| 7 Typical time to recover to 95% of bias value, typical cable compensation, Ibias>50% Max bias. |
| 8 Typical time to recover to 99.9% of bias value, typical cable compensation, Ibias>50% Max bias. |
| 9 Typical p-p current variation over 1 hour, after warm up at 23 C. |
| 10 Pulse Width Offset is a correction factor that is automatically added to the pulse width setting. By setting this factor, nominal pulse width errors can be reduced. The setting range for Pulse Width Offset is +/- 50 μs. |
| 11 Requires Force Sense Selector Switch option. |
| 12 Max compliance voltage, load inductance and forward voltage can impact pulse widths below 50 μs. |
| 13 Min period is 10 μs, 300 μs in Pulsed Sweep mode. Max period is 40 s for Pulsed Sweep, and Multiple Pulse modes. |
| 14 Typical Noise, RMS, 10 ms Measurement Aperture. |
Contact Us
Accurate currents combined with fast rise and fall times plus a precision hardware-controlled timing system that synchronizes source, measure and external instrumentation allow for discovery at low currents.
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