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Output Noise of LDC500/501 Current Source Rev B. Revised Oct 2012 Figure 1 Laser driver noise spectrum measurement setup LDC500 and LDC501 are equipped with an ultra We measure the output noise through a 25 low noise current source for laser diodes. The noise in resistor which converts the output current noise into a the output current is a combination result of thermal voltage noise which is then AC coupled to HP89410A noise (Johnson Noise) in resistors, shot noise in signal analyzer. Figure 1 shows the measurement semiconductors, flicker noise (1/f noise) , and setup. Figure 2 shows the measurement result. The electromagnetic interference (EMI) inside or outside output current was set at 50mA for LDC500 and of the instrument. The noise in the output current 100mA for LDC501. could be regarded as an addition to the setting current. Figure 2 Voltage noise and current noise measured across a 25 load driven by LDC500/LDC501 Stanford Research Systems www.thinksrs.com (408)744-9040 -1- In order to see details in the noise spectrum, the measurement limit of HP89410A, we added a gain measurement was divided into two bands: block of 100 before HP89410A and the measured 10Hz~10kHz and 10kHz~10MHz. Captured screens noise density is shown in the parenthesis. from HP89410A are cascaded at 10kHz as shown in Figure 2. During test, the LDC500 modulation input A comparative test was also done with a was disabled to reduce internal cable pickup. The competitor's controller, and the result is plotted in voltage noise is read close to 2kHz (Marker A, B, C and Figure 3. Both