Analog Discovery 2
- Qingqing Ni
Content
AD2 Overview
Digilent Analog Discovery 2 is a USB oscilloscope, logic analyzer, and multi-function instrument that allows users to measure, visualize, generate, record, and control mixed-signal circuits of all kinds. With AD2, you can test and debug your circuit outside the lab.
Tips
To connect the test probes, make sure you pushed the black bar all the way in. When the probes are properly connected, you should not see the metal contact points exposed.
Inputs and Outputs
Waveforms Software Functions
- Scope: Activate and configure the oscilloscope functions.
Probe the signal (e.g., input/output of the filter circuit) with 1+ or 2+. Once you click “Run”, the scope will start display signals captured.
You may connect 1-/2- to ground if noise presents.
- Wavegen: Activate and configure the waveform generator.
Configure the type of waveforms (Sine, Square, Triangle, Ramp, Pulse, etc.), the frequency (upto 10MHz), amplitude (upto 5V), offset, symmetry and phase. Once finished configuring, click “Run” to activate the wavegen. You can select “Channels” to feed the signal generated to either channel 1 (W1) or channel 2 (W2).
- Supplies: Activate and configure the variable supplies.
This panel allows you to configure the supplies output from “V+” and “V-”. You can adjust the voltage and click on “Master Enable is off” to enable the supplies. The “V+” and “V-” can be used as positive and negative supplies for the circuit, for example the OpAmp.
- Spectrum: Activate and configure the spectrum analyzer.
This panel allows you to observe the spectrum of a signal where the x-axis is the frequency and the y-axis is the amplitude in dB scale. Probe the signal (e.g., input/output of the filter circuit) with 1+ or 2+ and click “Run”, you can observe the power spectrum of the signal in frequency domain. As shown in the above figure, a dirac delta (δ) function at 0.2MHz is observed. This suggests the main signal component received is at 200kHz.
- Network: Activate and configure the network analyzer.
Network panel allows you to characterise the network transfer function, (i.e. obtain the Bode Plot). It will sweep a frequency input specify by the “Start” and “Stop” frequency, and measure the corresponding input and output waveforms as shown in the above figure. Adjust the “Amplitude” under “Wavegen” on the right to keep the signal from saturating the circuit. The yellow curve will be the measured signal corresponding to input (1+), and the cyan curve will be the measured signal amplitude corresponding to the output (2+) relative to the input. You can show the cursor by selecting the menu “View->Cursors”. By moving the vertical red line across the screen you can see the corresponding changes of readings for the C1 and C2. Stop the cursor when C2 shows a value of around -3dB. The corresponding “Position” reading will indicate the 3-dB cut-off frequency of the filter, which in this case shows 325Hz.
To explain the connection of AD2 to characterise the filter circuit, please refer to the passive filter example below:
Keep in mind that in order to characterise the frequency response, Wavegen probe(s) (W1/W2) is(are) required to be connected the input sweep signal. 1+ is probing the input to the filter, while 2+ is probing the output from the filter. Aware that this does NOT mean you need to run Wavegen function separately, the Network function will feed generated signal through the probes.
The ground probes are used to ground all probes as well as your circuit. All 4 ground wires are equivalent. Extremely high frequency generated by AD2 is unstable, if you see fluctuations towards 1 GHz, that is perfectly normal.
Refer to Lab 3 folder for video guide on how to obtain Bode Plot use Waveforms.
Record signal with Waveforms and AD2
Connection when recording signal from RTL-SDR
| AD2 | Hardware |
|---|---|
| 2+ | RTLSDR yellow wire |
| 2- | AD2-GND |
| GND | RTLSDR GND (connect wire yourself) |
Connection when recording signal from LPF circuit output
| AD2 | Circuit |
|---|---|
| 2+ | LPF circuit output |
| 2- | circuit GND |
| GND | circuit GND |
| V+ | circuit +Vcc |
| V- | circuit -Vcc |
Setting
- Select “Settings -> Device Manager -> Option 2 (2x16k)” to maximize the buffer size
- Change the “mode” to “Record”
- Click “Config”, choose “Samples” of “32768”, “Rate” of “4 MHz”, “Base” of “7.5ms”, and click “Start”
- You can repeatedly click “Record” button to capture the data.
- At the side panel, click “Options”, uncheck “noise”, click “Zero offset”
- Once done, select ”File -> Export”. Under “Data” tab, select “Save” and store the data into “test.csv”.
