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 $R_1 = 1k\Omega$ and $R_2 = 10 k\Omega$ as starting values.

2. insert a 0.1 $\mu$F capacitor between ground and the OP power supply input pin.

Gain measurements

1. Measure the gain as a function of frequency between 100 Hz and 2 MHz for three values of R_2 = 10 k$\Omega$, 100 k$\Omega$, 1M$\Omega$.
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 $R_{in}$ for the 10 fold and 100 fold amplifier at ~100 Hz and 10 kHz frequency.

Output Impedance

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

$V_{io}$ and $I_{B}$

$V_{out}= -\frac{R_1}{R_2} V_1 + \left ( 1 + \frac{R_1}{R_2}\right)V_{io} + R_2 I_B$

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

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

$I_{io}$

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

Instead of the current $I_B$ we have the current $I_{io}$

$V_{out}= -\frac{R_1}{R_2} V_1 + \left ( 1 + \frac{R_1}{R_2}\right)V_{io} + R_2 I_{io}$

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

The offset Null Circuit

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

Capacitors

Revert back to the pull up resistor

Capacitor in parallel with $R_2$

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

Capacitor in series with R_1

1. Select a capacitor such that$\frac{1}{\omega C_2} \approx R_1$ when $\omega$= 1 kHz.
2. Add the capacitor in series to $R_1$ so you have the circuit shown above.
3. Use a pulse generator to input a sinusoidal voltage $V_{in}$
4. Measure the Gain as a function of the $V_{in}$ 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 $V_{out}$ while changing $V_{cc}$

Output voltage RMS noise $\Delta V_{out}^{RMS}$

Forest_Electronic_Instrumentation_and_Measurement