1. Using the gain bandwidth product, find the bandwidth of the circuit below. Use the AOL curve and closed loop gain to graphically determine the bandwidth of this circuit. Find the bandwidth using an “ac transfer characteristic” simulation.

+18V-18V

+18V

-18V

+

Vin

RF 4.7kR1 1k

Vout

-

++V

U1 OPA188

V1 18 V2 18

Solutions

OPA188Data Sheet

1. The hand calculation for closed loop bandwidth gives BW = 351kHz. Note that the noninverting gain (also called noise gain) was used even though the amplifier is an inverting configuration.

Gn

Rf

R11

4.7k1k

1 5.7

BWGBW

Gn

2MHz

5.7351kHz

1. Using the AOL curve from the data sheet we can also estimate bandwidth. The estimate is very close to the calculated bandwidth.

0300-problem1.TSC

1. Using Tina Spice you can verify the bandwidth. Note that the simulated bandwidth is close but not exactly the same as the calculated bandwidth. The error may be from secondary effects (e.g. input capacitance) or model accuracy issues.