how to increase operational amplifier gain

[snishanth512]

Does the bandwidth decrease when I keep on increasing the value of the resistors for the attached circuit?

And does the bandwidth also depends on opamp ?

 

[ashugtiwari]

bandwidth does depend on op-amp. Look at the GBP (gain bandwidth product) parameter in op-amp datasheet. for eg. if the GBP is 1MHz for an op-amp, and if u give op-amp input as 1MHz ac signal, the open loop gain is 1 at that input frequency or more.
As far as i know, looking at ideal op-amp characteristics, the bandwisth depends on the GBP of op-amp IC. So, if ur input frequency is constant for say 10kHz, according 1MHz GBP, the max gain u can attain is 1M/1k = 100, irrespective of ur configured gain in ideal op-amp scenario.

 

[snishanth512]

if ur input frequency is constant for say 10kHz, according 1MHz GBP, the max gain u can attain is 1M/1k = 100, irrespective of ur configured gain in ideal op-amp scenario.

I didn't get it.

Can you suggest me a material (i.e. which explains your statement).

 

[chuckey]

your circuit is incomplete, there must be a series resistance to the -Ve input. Gain bandwidth product = G X b/w, gain = 10, b/w = 1MHZ/10 = 100KHZ, gain = 1000, b/w = 1MHZ/1000 = 1KHz. . .
Frank

 

[ashugtiwari]

Mr. Chuckey answered it in best mathematical way.
BTW, u ca read on op-amps from Linear IC's - by ramakant gayakwad. This book is good for beginners and explains all basics of op-amps in sweet, simple and short way. Then can go for more advanced books.
here is brief, an ideal op amp should have infinite bandwidth and infinite input impedance. It means it should work for any frequency i.e. 1Mhz or 1GHz, the output gain will be constant. The open loop gain is infinite. 0 output impedance. 0 offset voltage and current. 0 bias current. infinite CMRR.
but, in reality, op-amps have limited bandwidth, high imput impedance, low output impedance, high open loop gain. ANd the gain is dependant on what frequency are u operating. Gain is inversely proportional to frequency bandwidth. so, frequency increases, so is the gain decreases. But if freq is constant, maximum attainable gain is consta too which is found from GBP.

hope that helps.

 

[snishanth512]

First stage is IV converter.

No need for resistance.

I am going to connect phototransistor (QSE113).

Collector of photo transistor to 5V and emitter to the IV converter (inverting input).

Sorry for mention it along with my question.

 

[Audioguru]

The datasheet for an opamp shows its frequency response and slew rate.

The maximum gain of an OP07 opamp at DC to 1Hz is 1 million.
At 1kHz its max gain is 1000.
At 10kHz its max gain is 100 but the slew rate limits the output to only 8V p-p.