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LDC501 Current Source Response to Modulation Signals Rev B. Revised Oct 2012 Fig.1 Setup for LDC501 laser current source response to modulation input This application note shows some examples of the an oscilloscope. A 17.4 resistor is used as the load of LDC501's laser current source response to modulation the LDC501 laser current source, which is made with input signals. The experimental setup is shown in Fig.1. several resistors in parallel to achieve high power of over 4W. The voltage signal across this resistor is fed to The modulation signal from a function generator is Ch2 of the scope. Ch2 is inverted in order to easily fed into the LDC501 modulation input and the Ch1 of compare with input signal. Stanford Research Systems www.thinksrs.com (408)7449040 -1- 1. Sine and Triangle wave response In Fig.2 the LDC501 output current setpoint is 250mA. The blue trace is the input signal which is 100kHz and 6Vpp. The red trace is the output voltage across 17.4. The vertical axis is 0.87V/div which corresponds to 50mA/div (=0.87/17.4). Fig.2 LDC501's response to 100kHz Sine wave and triangle wave 2. Square wave and step response In Fig.3 the blue trace is the input square wave which is 100kHz and 6Vpp. The red trace is the output voltage across 17.4. The vertical axis is 0.87V/div which corresponds to 50mA/div. The rising edge is about 0.3us corresponding to 0.35/0.3 = 1.17MHz bandwidth. Fig.3 LDC501 response to 100kHz square wave and step response Stanford Research Systems www.thinksrs.com (408)7449040 -2- 3. Limited output In Fig.4 the output current setpoint is 250mA and current limit setting is 300mA. The blue trace is the modulation input signal whose amplitude is 6Vpp with 10kHz, 50kHz, 100kHz or 500kHz frequencies. The red traces are the output voltages across the 17.4 resistor load. The overshoot is dependent on the cable parasitic parameters and the slew rate of the input signal.