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This report evaluates the performance of Lock-in Amplifier(LIA) between OE1022 and SR830 by three different applications: 1. Grating spectrometer measurement on OE1021 and SR830; 2. Weak current measurement on OE1022 and SR830; 3. Performance report of SINE OUT function of OE1022-B(advanced OE1022).

We use OE1021 and SR830 respectively to measure one optical spectrum following the setting list below. The measurement result on Fig.1 and Fig.2 shows that the performances of both LIA are the same.

1) Parameters setting of LIA: 300ms, normal, 12dB, I(10^{6}), DC, FLOAT, 500nA.

2) Frequency of Optical Chopper: 1000Hz.

3) Slot Width: 3mm.

4)Sample frequency of collection card: 100S/s

5) Grating rotates 360 degree.

In Fig.1 and Fig.2, the blue line and the red line denotes the measurement result of SR830 and OE1021 respectively. The Fig.2 shows the details of Fig.1 from 1.55x10^{4} Hz to 1.9x10^{4} Hz.

Fig.1 Measurement results of OE1021 and SR830

Fig.2 Detailed measurement results of OE1021 and SR830

Fig.3 Measurement platform

Fig.4 Special current input connection

As Fig.3 shows, this experiment focus on the performance of the current input function of OE1022 of SSI and SR830 of STANFORD RESEARCH SYSTEMS. The current source is 6221 DC AND AC CURRENT SOURCE of KEITHLEY. Fig.4 shows the special current input connection in order to eliminate the input noise from BNC cables.

Please set OE1022 and SR830 follow the steps below.

1. Set input mode to “I”.

2. Set input amplitude to “1M” in OE1022 or “I(10^{6})” in SR830.

3. Set coupled mode to “AC” and ground mode to “Float”.

4. Set reference signal mode to “Internal”.

5. Set time constant to “300ms”, roll-off to “12dB/oct”.

6. Set dynamic reserve mode to “Normal”.

7. Set sensitivity value practically.

8. Others are default.

Please follow the order to set 6221 current source.

1. Set triax inner shield mode to “output low” and triax output low mode to “earth ground”.

2. Set output signal mode to “Sine” and the sine frequency to 1000 Hz.

3. Set compliance voltage to 1.00V.

4. Set the amplitude of sine output practically.

5. Others are default.

First, set the sine output amplitude of 6221 current source to 1.0000nA RMS or 1.4142nA PEAK and the sensitivity to 2nA.The measurement result is stored in 1nA-OE1022.avi and 1nA-SR830.avi.

Table.1 The measurement result of the fluctuation of current amplitude for 1nA input

Second, set the sine output amplitude of 6221 current source to 0.1000nA RMS and 0.0100nA RMS and the sensitivity to 200pA and 20pA respectively. The measurement result is stored in 100pA-OE1022.avi, 100pA-SR830.avi and 10pA-OE1022.avi, 10pA-SR830.avi.

Table.2 Measurement result of the fluctuation of current amplitude for 100pA input

Table.3 Measurement result of the fluctuation of current amplitude for 10pA input

Based on the platform in Fig.3 and the setting list in part 2, we also need to reset the sine output amplitude of 6221 current source to 0.0100nA RMS, and connect LIAs to PC through USB as Fig.5. In Fig.6 and Fig.7, the measurement result of current-time curve is collected by LabVIEW program.

Fig.5 Measurement platform

The average value and the standard deviation of the measurement result of the input current of OE1022 is 10.197pA and 0.37458pA. For SR830, the average value and the standard deviation is 10.202pA and 0.95835pA. More data are stored in 10pA-1kHz-OE1022.xls and 10pA-1kHz-SR830.xls.

Fig.6 Measurement result of OE1022 for 10pA input

Fig.7 Measurement result of SR830 for 10pA input

Fig.8 and Fig.9 shows that the stability of OE1022 is better than SR830 after many times of measurement at the same measurement platform. More data are stored in 10pA-1kHz-OE1022-Test1.xls, 10pA-1kHz-OE1022-Test2.xls, 10pA-1kHz-OE1022-Test3.xls, and 10pA-1kHz-SR830-Test1.xls, 10pA-1kHz-SR830-Test2.xls, 10pA-1kHz-SR830-Test3.xls.

Fig.8 Three tracks of the measurement result of OE1022

Fig.9 Three tracks of the measurement result of SR830

Based on the platform in Fig.5 and the setting list in part 2, this test also need to change some parameters as below:

1. Set the current output amplitude of 6221 current source to 1.0000nA RMS.

2. Set the current output frequency of 6221 current source to 1kHz, 5kHz, 10kHz.

3. Set time constant to 30ms and sensitivity to 2nA.

Fig.10, Fig.11 and Table.4 all show that, the current amplitude decreases with the increasing of frequency. More data are stored in 1nA-1kHz-OE1022.xls， 1nA-5kHz-OE1022.xls， 1nA-10kHz-OE1022.xls and 1nA-1kHz-SR830.xls， 1nA-5kHz-SR830.xls， 1nA-10kHz-SR830.xls.

Fig.10 Measurement result of the amplitude for 1nA input in different frequency using OE1022

Fig.11 Measurement result of the amplitude for 1nA input in different frequency using SR830

Table.4 Measurement result for 1nA input

Fig.12 Measurement result of the amplitude for 1nA input in 50kHz using OE1022

Fig.13 Measurement result of the amplitude for 1nA input in 50kHz using SR830

We set the frequency of current output to 50kHz and increase the sensitivity of LIA practically, then we get Fig.12 and Fig.13, which show that the average value of current measurement is larger than 1nA. The average value and the standard deviation of the current measurement for OE1022 are 3.1343nA, 78.716pA; for SR830, they are 4.5081nA, 564.60pA. More data shows in “1nA-50kHz-OE1022.xls” and “1nA-50kHz-SR830.xls”.

Fig.14 Measurement platform

In this test, we need to replace the current source by a photodiode because photodiode can get a low-SNR current signal. The amplitude of the light current through LIA can be changed by changing the angle of optical grating in monochromator.

The setting list is similar to part 2, but we need to change some of them:

1. Set the reference signal to “External”.

2. Open the sync filter.

3. Set roll-off to 24dB/oct.

4. Set time constant to 3s.

At the platform, the same current inputs OE1022 and SR830. And then the frequency changes from 20Hz to 190Hz by a optical chopper. The measurement result shows in Table 5.

Table.5 Measurement result of the current amplitude in low frequency sweeping

Fig.16 Amplitude-frequency curve of OE1022 and SR830

OE1022-B, which is an advanced version of OE1022, optimizes the performance of SINE OUT function of OE1022. The output amplitude of SINE OUT function can be set from 1mV RMS to 5V RMS, and the SNR value becomes higher.

In this test, we compare the performance of SINE OUT function of OE1022-B, SR830 and Agilent 33250A. The oscilloscope is DPO 4104B from Tek. The waveforms show in Fig.17, Fig.18, Fig.19 and Fig.20, where the yellow line is from OE1022-B, the blue line is from 33250A and the purple line is from SR830.

Fig.17 Waveform of 4mV RMS, 1kHz SINE OUT signal

Fig.18 Waveform of 4mV RMS, 100kHz SINE OUT signal

Fig.19 Waveform of 10mV RMS, 1kHz SINE OUT signal

Fig.20 Waveform of 10mV RMS, 100kHz SINE OUT signal

The result shows that OE1022-B performs as the same as Agilent 33250A, and better than SR830, especially in high frequency. The SINE OUT of SR830 has a larger burr in high frequency.