Part C. Analog RC filter analysis using the Bode Analyzer:

A bode plot defines the frequency characteristics of a given circuit. Magnitude response is plotted as circuit gain in

decibels as a function of log frequency. Phase response is plotted as the phase difference between input and output

signals on a linear scale as a function of log frequency. NI ELVIS has a bode analyzer SFP which facilitates

automatic bode plot generation of a given circuit. Complete the following steps to obtain the Magnitude and

Phase response of the RC filter:

1.

Retain the circuit configuration from the previous section. Note that the circuit should be setup as shown

in figure 11.

2.

Ensure that the connections are correct and switch the prototype board power to ON position.

3.

From the NI ELVIS instrument Launcher, select Bode Analyzer. The initial Bode Analyzer SFP should

appear as shown in figure 17.

4.

Bode analyzer controls the input signal to the circuit from the FGEN ports. The output signal to be analyzed

should be connected to Analog Channel 0 (between AI0+/AI0-). The input signal should also be

connected to Analog channel 1 (between AII+/AII-).

5. Bode analyzer provides the flexibility to automatically scan the input signal frequency over a range

specified by Start/Stop frequency values. The incremental value used during this frequency scan can also

be set to a specific value. All these controls can be seen in figure 18.

6. For analyzing the RC low pass filter, let's make the following settings on the Bode analyzer SFP.

7.

8.

Start frequency to 10 Hz.

Stop frequency to 100 KHz.

Steps to 20 per decade (Higher the number of steps, greater the number of points for the measurement accuracy).

Display section, set Y-scale to Auto.

Click on RUN.

Once the analysis is complete, the output should appear as shown in figure 19.

In the figure 18, cursor has been placed to measure the -3dB frequency. This can be achieved by clicking

on the Cursors button to "ON" and dragging the cursor using the left mouse button on the plot to the

desired position. The cursor can also be shifted to the desired position using the two diamond shaped

buttons in the Cursor Position/nBode Analyzer - NI ELVISmx

Phase (des)

LabVIEW

0.8-

0.6

0.2

0.0-

-0.4

-0.6-

0.8

-LO

25.0

20.0

15.0

Phase (deg)

10.0

5.0

0.0

-5.0

-10.0

-15.0

Frequency (t) 0.00

(ap)

Bode Analyzer - NI ELVISmx

LabVIEW

0.0-

-2.5

-5.0

-10.0-

-12.5-

-15.0-

-17.5

-22.5-

0.0-

-30.0

-20.0

80.0

Connections: SCOPE CHO-FGEN SCOPE CH 1 - Signal

10

1000

Frequency (Hz)

1000

Frequency (H₂)

Phase (deg) 0.00 Gain 0.00 Gain (8) Inf

1000

Frequency (tr)

Connections: AI 1-FGEN ATO-Signal

1000

Frequency)

Frequency (Hz) 5623.33 Phase (deg) 43.83 Gain 0.72

10000

10000

10000

10000

Gain (d) -2.89

100000

Measurement Settings

Stimulus Channel

SCOPE CHO

100000

Start Frequency

100.00ⒸH

Stop Frequency

Fig.18. Uninitialized NI ELVIS Bode Analyzer window.

10.00kr

Steps

Peak Amplitude

2.00

5 per decade)

Graph Settings

Mapping

Logarithmic

Cursor Settings

Cursors On

Cursor (Real)

Instrument Control

Device

Devi (NI ELVIS II+)

Start Frequency

10.00ⒸH

Stepe

Response Channel

SCOPE CH 1

Stop Frequency

300.00k

Stop Print Log Help

Measurement Settings

Stimulus Channel Response Channel

AL 1

ATO

Peak Amplitude

2.00

Op-Amp

Signal Polarity

Normal

Graph Settings

Mapping

Logarithmic

✔Autoscale

Position

Left◆◆ Right

20(per decade)

Cursors On

Cursor (Real)

Instrument Control

Op-Amp

Signal Polarity

Normal

Autoscale

Position

Left →→ Right

Dev10 ELVIS 114)

Run Stop Print Log Help

B