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[chenjk09]

Hi,

I like to understand this circuit shown in the link below
https://www.electro-tech-online.com/custompdfs/2012/06/opa344.pdf

FIGURE 7
where is the Passband in the circuit?
how is the gain set?

 

[WTP Pepper]

If you are referring to Fig 7 then it's a combination of the mic amp gain (1st half R6 & R7) which is text book op-amp gain equations and the gain of the filter (2nd half) which is a multiple feedback filter which is better simluted using LTSpice and redesigned using the TI Filterpro (I think that's the name) software and resimulated.

As a mic amp I would add some soft clipping using diodes and a resistor in parallel in the feedback of the mic amp. It reduces the harshness of the sound when overloaded.

 

[chenjk09]

is there any anaylitical equation?
I want to do the Calculation for gain and passband.
from the cct can see that is non-inverting amplifier. negative feedback
G = 1 + R9/R7 = 11 ? <-- is this correct??
anyone can teach me here?
Ref:
https://en.wikipedia.org/wiki/Opamp

 

[WTP Pepper]

https://www.electro-tech-online.com/custompdfs/2012/06/sbfa001c.pdf

Look at page 10. Your circuit is there. Download the software and play.

Hand analysis of such circuits is very complex and maybe above your skills from your postings. Analysis requires summing of admitances at each node of the circuit and mapping it to a S transform equivalent of a band pass filter. When I was in education, this here in the UK was final year degree stuff.

However thanks to TI and LTSpice, you don't have to worry about it. We refer to it as "Botch & Scarper"

 

[chenjk09]

View attachment 65235
Thank
Any advice?

 

[chenjk09]

The right side of the amplifier gives a gain of -10. shown in the img.

How to calculate the left side of the amplifier?

Where is the passband filter of the circuit?

 

[audioguru]

The left opamp is non-inverting so its voltage gain is (100k/10k) +1= 11.

You can simply calculate the cutoff frequency of each coupling capacitor for low frequencies then simply calculate the cutoff frequency of the second-order lowpass filter for high frequencies.

 

[chenjk09]

Thank for the reply.
How do I find the total gain?
Left opamp gain * right opamp gain?
Gain = 6 * -10 = -60
Not equal gain of 100.
Ref: https://www.electro-tech-online.com/custompdfs/2012/06/1504678.pdf
FIGURE 7. Speech Bandpass Filtered Data Acquisition System

 

[audioguru]

The lowpass filter (the opamp at the right) is a complicated Multiple-feedback type. Its gain is shown here:
https://www.electro-tech-online.com/custompdfs/2012/06/sboa114.pdf

 

[chenjk09]

Base on the data sheet
https://www.electro-tech-online.com/custompdfs/2012/06/opa344.pdf

A SPICE macromodel for
design analysis is available for download from www.ti.com.

Where can I download the SPICE software?

I download LTSpiceIV and PSpice student

LTSpiceIV how to load OPA2344 component?

Which is the correct software?

Thank

 

[chenjk09]

I like to connect up the Figure 7. Speech Bandpass filtered Data Acquisition System.
what is the correct software?

 

[audioguru]

I like to connect up the Figure 7. Speech Bandpass filtered Data Acquisition System.
what is the correct software?

The simple circuit uses the opamps well within the spec's of ANY opamp so you can simulate it with ANY opamp.

The opamp is Cmos so it has an infinite input impedance. Opamps with normal transistor inputs also have a very high input impedance.
The opamp has a typical gain of about 300 at 3kHz but the circuit goes to only 3kHz.
The opamp slew rate is high enough to go much higher (90kHz) than the required 3kHz. A very slow LM358 dual opamp has trouble above 2kHz.

 

[chenjk09]

View attachment 65349
How to set this opamp..
any opamp so i use LM358 will also get the same result?
exmaple 300 and 3khz?

The simple circuit uses the opamps well within the spec's of ANY opamp so you can simulate it with ANY opamp.

The opamp is Cmos so it has an infinite input impedance. Opamps with normal transistor inputs also have a very high input impedance.
The opamp has a typical gain of about 300 at 3kHz but the circuit goes to only 3kHz.
The opamp slew rate is high enough to go much higher (90kHz) than the required 3kHz. A very slow LM358 dual opamp has trouble above 2kHz.

 

[audioguru]

The datasheet for the LM358 shows that it is noisy and its max input bias current is too high for 1M ohm biasing resistors.
Its max output is only +3.8V when its supply is +5.0V.
With a +5.0V supply it performs fine at 3kHz.

 

[chenjk09]

Hi,

link shown below is OPA2344.
https://www.electro-tech-online.com/custompdfs/2012/07/opa344.pdf

 

[chenjk09]

thank,
but is OPA2344 not LM358

 

[chenjk09]

Hi,

thank for the reply.
how about the right opamp?
base on the link below it is Multiple Feedback (MFB). (page 10 figure 12)
Gain =-(R2/R1) = - (R9/R7) = - (510K/51K)
=-10
https://www.electro-tech-online.com/custompdfs/2012/08/sbfa001c.pdf

my question is why gain have "-"

I tested out the left opamp at pin 1 it give me a gain of 11.111 (Vmax=4.08V)
but for pin 7 i get 5.04V

Input Ampl : 200mV
Input Freq : 2kHz

pin 7 Vmax = 5.04V
gain = 5.04/ 200mv = 25.2

The left opamp is non-inverting so its voltage gain is (100k/10k) +1= 11.

You can simply calculate the cutoff frequency of each coupling capacitor for low frequencies then simply calculate the cutoff frequency of the second-order lowpass filter for high frequencies.

 

[chenjk09]

Hi guys base on the data sheet figure 7. The G = 100.

Gain = 100. ?

Can I say the output of the last op-amp = Vin * 100 = Vout?
Is it any input will * 100 ?

What is the G mean? Measure in AC or DC? How can I measure the G = 100?
Thank

 

[audioguru]

The total AC voltage gain of the two opamps is 100. The voltage gain of the left opamp is 100k/10k= 10 and the voltage gain of the right opamp is 510k/51k= 10.

The circuit is a bandpass filter so only frequencies in the bandpass (300Hz to 3kHz) will have a voltage gain of 100. Lower frequencies and higher frequencies will have much less gain.

Feed 1khz at 5mV RMS to the input and measure 0.5V RMS at the output.

 

[chenjk09]

Hi,
I try to give an output from Function Generator of 5mV the noise level very high.

The total AC voltage gain of the two opamps is 100. The voltage gain of the left opamp is 100k/10k= 10 and the voltage gain of the right opamp is 510k/51k= 10.

The circuit is a bandpass filter so only frequencies in the bandpass (300Hz to 3kHz) will have a voltage gain of 100. Lower frequencies and higher frequencies will have much less gain.

Feed 1khz at 5mV RMS to the input and measure 0.5V RMS at the output.