Lab 23 TF EIM

Inverting OP Amp

1. Construct the inverting amplifier according to the wiring diagram below.

Here is the data sheet for the 741 Op Amp

File:LM741CN OpAmp.pdf

Use [math]R_1 = 1k\Omega[/math] and [math]R_2 = 10 k\Omega[/math] as starting values.

2. Insert a 0.1 [math]\mu[/math]F capacitor between ground and both Op Amp power supply input pins.

Gain measurements

1.) Measure the gain as a function of frequency between 100 Hz and 2 MHz for three values of [math]R_2[/math] = 10 k[math]\Omega[/math], 100 k[math]\Omega[/math], 1M[math]\Omega[/math]. Keep [math]R_1[/math] at [math]1k\Omega[/math].

2.)Graph the above measurements with the Gain in units of decibels (dB) and with a logarithmic scale for the frequency axis.

Impedance

Input Impedance

1. Measure [math]R_{in}[/math] for the 10 fold and 100 fold amplifier at ~100 Hz and 10 kHz frequency.

Output Impedance

1. Measure [math]R_{out}[/math] for the 10 fold and 100 fold amplifier at ~100 Hz and 10 kHz frequency. Be sure to keep the output ([math]V_{out}[/math]) undistorted

[math]V_{io}[/math] and [math]I_{B}[/math]

[math]V_{out}= -\frac{R_1}{R_2} V_1 + \left ( 1 + \frac{R_1}{R_2}\right)V_{io} + R_2 I_B[/math]

Use the above equation and two measurements of [math]V_{out}[/math], [math]R_1[/math], and [math]R_2[/math] to extract [math]V_{io}[/math] and [math]I_B[/math].

1. measure [math]V_{out}[/math] for [math]R_1[/math] = 1 k[math]\Omega[/math], [math]R_2[/math] = 100 k[math]\Omega[/math], and[math] V_{in}[/math]=0 (grounded).
2. measure [math]V_{out}[/math] for [math]R_1[/math] = 10 k[math]\Omega[/math], [math]R_2[/math] = 1 M[math]\Omega[/math], and[math] V_{in}[/math]=0 (grounded).
3. You can now construct 2 equations with 2 unknowns [math]V_{out}[/math] and [math]I_B[/math].

[math]I_{io}[/math]

Now we will put in a pull up resistor R_3 as shown below.

Instead of the current [math]I_B[/math] we have the current [math]I_{io}[/math]

[math]V_{out}= -\frac{R_1}{R_2} V_1 + \left ( 1 + \frac{R_1}{R_2}\right)V_{io} + R_2 I_{io}[/math]

Use the same technique and resistors from the previous section to construct 2 equations and 2 unknowns and extract [math]I_{io}[/math], keep [math]V_{in}[/math]=0.

The offset Null Circuit

1. Construct the offset null circuit above.
2. Adjust the potentiometer to minimize [math]V_{out}[/math] with [math]V_{in}=0[/math].
3. Use a scope to measure the output noise.

Capacitors

Revert back to the pull up resistor

Capacitor in parallel with [math]R_2[/math]

1. Select a capacitor such that[math] \frac{1}{\omega C_2} \approx R_2[/math] when [math]\omega[/math]= 10 kHz.
2. Add the capacitor in parallel to [math]R_2[/math] so you have the circuit shown above.
3. Use a pulse generator to input a sinusoidal voltage [math]V_{in}[/math]
4. Measure the Gain as a function of the [math]V_{in}[/math] frequency and plot it.

Capacitor in series with R_1

1. Select a capacitor such that[math] \frac{1}{\omega C_2} \approx R_1[/math] when [math]\omega[/math]= 1 kHz.
2. Add the capacitor in series to [math]R_1[/math] so you have the circuit shown above.
3. Use a pulse generator to input a sinusoidal voltage [math]V_{in}[/math]
4. Measure the Gain as a function of the [math]V_{in}[/math] frequency and plot it.

Slew rate

Measure the slew and compare it to the factory spec.

Power Supply Rejection Ratio

1. Set V_{in} = 0.
2. Measure [math]V_{out}[/math] while changing [math]V_{cc}[/math]

Output voltage RMS noise [math]\Delta V_{out}^{RMS}[/math]

Forest_Electronic_Instrumentation_and_Measurement