EE 420L Engineering Electronics II Lab 

Lab 4- Op–amps II, gain-bandwidth product and slewing

 

Francisco Mata Carlos

 email: matacarl@unlv.nevada.edu

 2/27/19

 

Pre-lab:

 

Lab description:

 The goal of this lab is to test for different gains using inverting and non-inverting topologies and experimentally find bandwidths and slew rate.

 

Experiment 1:

Estimate, using the datasheet, the bandwidths for non-inverting op-amp topologies having gains of 1, 5, and 10.

 

   

The plot and information above show the open loop gain and the Gain Bandwidth Product. This applies to voltages of VCC =30V, and 10V to 15V. We are using VCC = 5V and VCC- = 0V. so it seems that. For the hand calculations we are using 1.3MHz as GBW product to make estimates, and then show the results experimentally.

 

NON-Inverting topology

LtSpice Simulations

 

Experiments Results

 

Hand Calculations

GBW = 1.3MHz

Gain =1

Gain=1

 

 

Input (yellow) = 100mVpp

(100mVpp)*(1) = 100mVpp

Output (blue) ≃ 70mVpp

 

Comments: The output seems to be lagging or having a phase shift. This is due to the Slew Rate (SR), which is 400mV/𝞵s.

The frequency to maintain the change in voltage is about 65KHz

 

GBW = 1.3MHz

 

 


 

 

      

Gain =5

Gain =5

 

 

 

 

 

Input (yellow) = 20mVpp

(input)*(gain) = output voltage

(20mVpp)*(5) = 100mVpp

3dB Output (blue) ≃ 70mVpp

 

 

Comments: The lagging again is due to the Slew Rate (SR), which is 400mV/𝞵s. The frequency to maintain the change in voltage is about 65KHz. The frequency difference from the hand calculations and experiments results seems to be related to the VCC voltage we are using. The smaller the VCC the lower the Bandwidths seem to be. The open-loop frequency response plot shown in the beginning with a 1.3MHz GBW seems to be calculated with VCC of 30V, however we are using 5V for VCC.

 

 

 

 



 

 

 

 

 

Gain = 10

 

Gain = 10

 

 

 

 

Input (yellow) = 20mVpp

(input)*(gain) = output voltage

(20mVpp)*(10) = 200mVpp

3dB Output (blue) ≃ 144mVpp

 

 

Comments: The frequency difference from the hand calculations and experiments results seems to be related to the VCC voltage we are using. The smaller the VCC the lower the Bandwidths seem to be. The open-loop frequency response plot shown in the beginning with a 1.3MHz GBW seems to be calculated with VCC of 30V, however we are using 5V for VCC.

 

 

 



 

 

 

 

 

 

Experiment 2:

Estimate, using the datasheet, the bandwidths for inverting op-amp topologies having gains of -1, -5, and -10.

 

Inverting topology

LtSpice Simulations

 

Experiments Results

 

Hand Calculations

GBW = 1.3MHz

Gain =1

Gain=1

 

 

 

 

 

Input (yellow) = 100mVpp

(input)*(gain) = output voltage

(100mVpp)*(-1) = -100mVpp

3dB Output (blue) ≃ -70mVpp

 

Comment: The 3dB was found at a frequency of about 5.7MHz. Not sure how this happen, but perhaps we did not account for other factors.

 

 

 

 


 

    

Gain =5

Gain =5

 

 

 

 

 

 

Input (yellow) = 20mVpp

(input)*(gain) = output voltage

(20mVpp)*(-5) = -100mVpp

3dB Output (blue) ≃ -70mVpp

 

 

Comment: The 3dB output voltage was found by using a frequency of about 225kHz, but the oscilloscope was not able to read this frequency.

 

 

 


 

    

 

Gain = 10

 

Gain = 10

 

 

 

 

 

Input (yellow) = 20mVpp

(input)*(gain) = output voltage

(20mVpp)*(-10) = -200mVpp

Output (blue) ≃ -144mVpp

 

Comment: The 3dB output voltage was found by using a frequency of about 108kHz, but the oscilloscope was not able to read this frequency.

 

 

 

 

 


 

    

 

 

 

Experiment 3:

Design two circuits for measuring the slew-rate of the LM324. One circuit should use a pulse input while the other should use a sinewave input

The snapshot above is from the datasheet which shows the Slew Rate (SR) to 400mV/𝞵s

The next set of calculations were used to find the slew rate frequency.

 

 

 

Sinewave  

Squarewave

1Vpp, 10kHz,  No Slew  Rate Shown

1Vpp, 30kHz,  Some Slew  Rate Shown

 

1Vpp, 170kHz, Slew Rate shown

1Vpp, 170kHz, Slew Rate shown

 

Because the slew frequency is about 63.7kHz for 1V, the output in picture above looks like a triangular wave because the frequency being used is 170kHz, and the op-amp is not able to keep up with the speed.

 

The image above shows, again, a triangular wave because the frequency is much higher than the slew frequency calculated above of about 63.7kHz. Thus, the op-amp is not able to keep up with the speed.

 

SR =

 


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