60mV to 10V voltage amplifier

Allen Bong · May 4, 2010

Hello group,

I wish to construct a circuit to amplify an input voltage of 0 to
60mV dc to output 0 to 10V linearly.
I have came out with a simple circuit as below:

TL084
0-60mV TL084
input |\ TL084
o-o------|+\ |\
| | | >---o--------|+\ |\ 0-10V
V - +--|-/ | | >----o----------|+\ output
- ^ | |/ | +--|-/ | | >----o----o
| | | | | |/ | | +--|-/ | |
o-o | ___ | | ___ | |100K | |/ | /+\
| +--|___|--+ +---|___|--+ preset| | ( )
| | 190k | 47K +--------- + \-/
| .-. .-. |
| | | | | |
GND | |10k | |10k ===
'-' '-' GND
| |
GND GND
----o-----o--------- +24V
Vcc op amp | |
.-. |+
R1 | | ===
10k | | /-\ 100uF
'-' |
| |
GND ----o-----o
| |
.-. |+
R2 | | ===
10K | | /-\ 100uF
'-' |
Vss op amp | |
----o-----o---------0V

(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

The first op-amp amplifies the signal by 20 and the second op-amp
amplifies the output by 5-15 times. The third stage is a buffer.
The op-amp used is a TI TL084. I was wondering if it is a good
idea to just amplify the 60mV by 166 in one stage followed by the
buffer. Would that cause any unstabilities? In that case I may
use TL082 instead.

I also have other op-amps like mc1458, lm748, lm358, lm324 and
TL071. Is TL084 a good choice in this particular circuit?

As for the power supply. I have only +24V DC from a battery.
Would the value of R1 and R2 be OK for the circuit to work?

Thanks,

Allen

Bob Masta · May 4, 2010

On Tue, 4 May 2010 00:35:32 -0700 (PDT), Allen
Bong <allenbsf6502@gmail.com> wrote:

Hello group,

I wish to construct a circuit to amplify an input voltage of 0 to
60mV dc to output 0 to 10V linearly.
I have came out with a simple circuit as below:

TL084
0-60mV TL084
input |\ TL084
o-o------|+\ |\
| | | >---o--------|+\ |\ 0-10V
V - +--|-/ | | >----o----------|+\ output
- ^ | |/ | +--|-/ | | >----o----o
| | | | | |/ | | +--|-/ | |
o-o | ___ | | ___ | |100K | |/ | /+\
| +--|___|--+ +---|___|--+ preset| | ( )
| | 190k | 47K +--------- + \-/
| .-. .-. |
| | | | | |
GND | |10k | |10k ===
'-' '-' GND
| |
GND GND
----o-----o--------- +24V
Vcc op amp | |
.-. |+
R1 | | ===
10k | | /-\ 100uF
'-' |
| |
GND ----o-----o
| |
.-. |+
R2 | | ===
10K | | /-\ 100uF
'-' |
Vss op amp | |
----o-----o---------0V

(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

The first op-amp amplifies the signal by 20 and the second op-amp
amplifies the output by 5-15 times. The third stage is a buffer.
The op-amp used is a TI TL084. I was wondering if it is a good
idea to just amplify the 60mV by 166 in one stage followed by the
buffer. Would that cause any unstabilities? In that case I may
use TL082 instead.

I also have other op-amps like mc1458, lm748, lm358, lm324 and
TL071. Is TL084 a good choice in this particular circuit?

As for the power supply. I have only +24V DC from a battery.
Would the value of R1 and R2 be OK for the circuit to work?

Thanks,

Allen

A couple of points: It's not clear what your
overall goal is here, but with an overall gain of
167 you are probably going to need to be concerned
with offset voltage and drift in the op-amps.

I don't know what the final load is supposed to
be, but I presume this is for some sort of
measurement. If so, and offset and drift are
problems, you could consider a "chopper" circuit:
Extend the front fork... oops, wrong chopper!
Seriously, the way to beat offset/drift in high
gain circuits is to "chop" the input signal to
make it into a square wave, then amplify it with
AC gain stages and measure the peak-to-peak
output. Lots of options here.

Note that this approach eliminates problems due to
intrinsic op-amp offset and drift, but does
nothing for gain drift due to resistor thermal
effects, etc.

Regarding the power supply, you should consider
using one op-amp as a "ground splitter". You
should consider this whether you go with your
original cicuit, or something fancier with a
chopper. Instead of the circuit you show, use 2
equal-valued resistors (10k is OK) to divide the
24V as shown, then feed that to an op-amp buffer
that drives the "ground" for the rest of the
circuit. You probably don't need the 100uF caps
on the divider, just a single smaller cap from the
12V midpoint to the true input ground... maybe
0.1uF, just to keep noise down.

Best regards,

Bob Masta

DAQARTA v5.10
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
Frequency Counter, FREE Signal Generator
Pitch Track, Pitch-to-MIDI
DaqMusic - FREE MUSIC, Forever!
(Some assembly required)
Science (and fun!) with your sound card!

keithw86@gmail.com · May 4, 2010

On May 4, 2:35 am, Allen Bong <allenbsf6...@gmail.com> wrote:

Hello group,

I wish to construct a circuit to amplify an input voltage of 0 to
60mV dc to output 0 to 10V linearly.

What is the frequency of your signal?

I have came out with a simple circuit as below:

TL084
0-60mV TL084
input |\ TL084
o-o------|+\ |\
| | | >---o--------|+\ |\ 0-10V
V - +--|-/ | | >----o----------|+\ output
- ^ | |/ | +--|-/ | | >----o----o
| | | | | |/ | | +--|-/ | |
o-o | ___ | | ___ | |100K | |/ | /+\
| +--|___|--+ +---|___|--+ preset| | ( )
| | 190k | 47K +--------- + \-/
| .-. .-. |
| | | | | |
GND | |10k | |10k ==> '-' '-' GND
| |
GND GND
----o-----o--------- +24V
Vcc op amp | |
.-. |+
R1 | | ==> 10k | | /-\ 100uF
'-' |
| |
GND ----o-----o
| |
.-. |+
R2 | | ==> 10K | | /-\ 100uF
'-' |
Vss op amp | |
----o-----o---------0V

(created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de)

The first op-amp amplifies the signal by 20 and the second op-amp
amplifies the output by 5-15 times. The third stage is a buffer.

*Generally* it's a good idea to put all the gain in one stage. The
only reason for not doing this is if you run into gain-bandwidth
problems with one stage.

The op-amp used is a TI TL084. I was wondering if it is a good
idea to just amplify the 60mV by 166 in one stage followed by the
buffer. Would that cause any unstabilities? In that case I may
use TL082 instead.

Shouldn't be an issue, though inputs and outputs shouldn't be routed
together. Depending on the bandwidth of your signal, you should put a
cap across the feedback resistors. It doesn't take much to kill any
chance of oscillation.

I also have other op-amps like mc1458, lm748, lm358, lm324 and
TL071. Is TL084 a good choice in this particular circuit?

No, that's a particularly bad choice for your circuit. The input
offset voltage on that part is 20mV! That's 1/3 of your full scale
signal. Not good. You should easily be able to find something with
one or two millivolts of input offset.

As for the power supply. I have only +24V DC from a battery.
Would the value of R1 and R2 be OK for the circuit to work?

It's going to be noisy, but it should work. You might add another

opamp in a voltage follower configuration to buffer this point. Also,
add a couple of .1uf caps (and maybe even lower values also) in
parallel with the 100uF caps. Another step would be to use this
additional opamp as an active filter for your bias network.

George Jefferson · May 5, 2010

"Allen Bong" <allenbsf6502@gmail.com> wrote in message
news:7041d68b-b2bf-47cb-9382-45a905c57642@34g2000prs.googlegroups.com...

Hello group,

I wish to construct a circuit to amplify an input voltage of 0 to
60mV dc to output 0 to 10V linearly.
I have came out with a simple circuit as below:

TL084
0-60mV TL084
input |\ TL084
o-o------|+\ |\
| | | >---o--------|+\ |\ 0-10V
V - +--|-/ | | >----o----------|+\ output
- ^ | |/ | +--|-/ | | >----o----o
| | | | | |/ | | +--|-/ | |
o-o | ___ | | ___ | |100K | |/ | /+\
| +--|___|--+ +---|___|--+ preset| | ( )
| | 190k | 47K +--------- + \-/
| .-. .-. |
| | | | | |
GND | |10k | |10k ===
'-' '-' GND
| |
GND GND
----o-----o--------- +24V
Vcc op amp | |
.-. |+
R1 | | ===
10k | | /-\ 100uF
'-' |
| |
GND ----o-----o
| |
.-. |+
R2 | | ===
10K | | /-\ 100uF
'-' |
Vss op amp | |
----o-----o---------0V

(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

The first op-amp amplifies the signal by 20 and the second op-amp
amplifies the output by 5-15 times. The third stage is a buffer.
The op-amp used is a TI TL084. I was wondering if it is a good
idea to just amplify the 60mV by 166 in one stage followed by the
buffer. Would that cause any unstabilities? In that case I may
use TL082 instead.

I also have other op-amps like mc1458, lm748, lm358, lm324 and
TL071. Is TL084 a good choice in this particular circuit?

As for the power supply. I have only +24V DC from a battery.
Would the value of R1 and R2 be OK for the circuit to work?

Thanks,

Allen

Why not use an instrumentation op amp configuration?

http://en.wikipedia.org/wiki/Instrumentation_amplifier

You can buy single packages that do it all for you.

Allen Bong · May 5, 2010

On May 4, 9:02 pm, N0S...@daqarta.com (Bob Masta) wrote:

On Tue, 4 May 2010 00:35:32 -0700 (PDT), Allen

Bong <allenbsf6...@gmail.com> wrote:
Hello group,

I wish to construct a circuit to amplify an input voltage of 0 to
60mV dc to output 0 to 10V linearly.
I have came out with a simple circuit as below:

TL084
0-60mV TL084
input |\ TL084
o-o------|+\ |\
| | | >---o--------|+\ |\ 0-10V
V - +--|-/ | | >----o----------|+\ output
- ^ | |/ | +--|-/ | | >----o----o
| | | | | |/ | | +--|-/ | |
o-o | ___ | | ___ | |100K | |/ | /+\
| +--|___|--+ +---|___|--+ preset| | ( )
| | 190k | 47K +--------- + \-/
| .-. .-. |
| | | | | |
GND | |10k | |10k ==> > '-' '-' GND
| |
GND GND
----o-----o--------- +24V
Vcc op amp | |
.-. |+
R1 | | ==> > 10k | | /-\ 100uF
'-' |
| |
GND ----o-----o
| |
.-. |+
R2 | | ==> > 10K | | /-\ 100uF
'-' |
Vss op amp | |
----o-----o---------0V

(created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de)

The first op-amp amplifies the signal by 20 and the second op-amp
amplifies the output by 5-15 times. The third stage is a buffer.
The op-amp used is a TI TL084. I was wondering if it is a good
idea to just amplify the 60mV by 166 in one stage followed by the
buffer. Would that cause any unstabilities? In that case I may
use TL082 instead.

I also have other op-amps like mc1458, lm748, lm358, lm324 and
TL071. Is TL084 a good choice in this particular circuit?

As for the power supply. I have only +24V DC from a battery.
Would the value of R1 and R2 be OK for the circuit to work?

Thanks,

Allen

A couple of points: It's not clear what your
overall goal is here, but with an overall gain of
167 you are probably going to need to be concerned
with offset voltage and drift in the op-amps.

I don't know what the final load is supposed to
be, but I presume this is for some sort of
measurement. If so, and offset and drift are
problems, you could consider a "chopper" circuit:
Extend the front fork... oops, wrong chopper!
Seriously, the way to beat offset/drift in high
gain circuits is to "chop" the input signal to
make it into a square wave, then amplify it with
AC gain stages and measure the peak-to-peak
output. Lots of options here.

Note that this approach eliminates problems due to
intrinsic op-amp offset and drift, but does
nothing for gain drift due to resistor thermal
effects, etc.

Regarding the power supply, you should consider
using one op-amp as a "ground splitter". You
should consider this whether you go with your
original cicuit, or something fancier with a
chopper. Instead of the circuit you show, use 2
equal-valued resistors (10k is OK) to divide the
24V as shown, then feed that to an op-amp buffer
that drives the "ground" for the rest of the
circuit. You probably don't need the 100uF caps
on the divider, just a single smaller cap from the
12V midpoint to the true input ground... maybe
0.1uF, just to keep noise down.

Best regards,

Bob Masta

DAQARTA v5.10
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
Frequency Counter, FREE Signal Generator
Pitch Track, Pitch-to-MIDI
DaqMusic - FREE MUSIC, Forever!
(Some assembly required)
Science (and fun!) with your sound card!- Hide quoted text -

- Show quoted text -

Hi Bob,

Thanks for your reply and recommendations. The input of the circuit
is a current sensor which outputs 60mV DC when the current is
maximum. The output of the circuit goes to a 10V volt meter. Yes it
is used for some sort of measurment.

I have googled on chopper circuit and came across this link

http://www.national.com/an/AN/AN-79.pdf

It says that a good low drift preamp like LM121 would be an
alternative for a chopper solution as you suggested. But I cant seem
to find the datasheet for LM121 even in my 1982 NS linear databook. I
would like to know the gain of this device to see if I can make use of
it.

Googling "ground splitter" finally get me to "Virtual ground
circuits"

http://tangentsoft.net/elec/vgrounds.html

I never knew that there are so many ways to do it even with
transistors. I picked the one with op-amp as you suggested.

Thanks and regards.

Allen

Allen Bong · May 5, 2010

On May 4, 9:14 pm, "keith...@gmail.com" <keith...@gmail.com> wrote:

On May 4, 2:35 am, Allen Bong <allenbsf6...@gmail.com> wrote:

Hello group,

I wish to construct a circuit to amplify an input voltage of 0 to
60mV dc to output 0 to 10V linearly.

What is the frequency of your signal?

I have came out with a simple circuit as below:

TL084
0-60mV TL084
input |\ TL084
o-o------|+\ |\
| | | >---o--------|+\ |\ 0-10V
V - +--|-/ | | >----o----------|+\ output
- ^ | |/ | +--|-/ | | >----o----o
| | | | | |/ | | +--|-/ | |
o-o | ___ | | ___ | |100K | |/ | /+\
| +--|___|--+ +---|___|--+ preset| | ( )
| | 190k | 47K +--------- + \-/
| .-. .-. |
| | | | | |
GND | |10k | |10k ==> > '-' '-' GND
| |
GND GND
----o-----o--------- +24V
Vcc op amp | |
.-. |+
R1 | | ==> > 10k | | /-\ 100uF
'-' |
| |
GND ----o-----o
| |
.-. |+
R2 | | ==> > 10K | | /-\ 100uF
'-' |
Vss op amp | |
----o-----o---------0V

(created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de)

The first op-amp amplifies the signal by 20 and the second op-amp
amplifies the output by 5-15 times. The third stage is a buffer.

*Generally* it's a good idea to put all the gain in one stage. The
only reason for not doing this is if you run into gain-bandwidth
problems with one stage.

The input signal is DC. So it's ok to amplify the signal by 167 in
one stage as it is DC.

The op-amp used is a TI TL084. I was wondering if it is a good
idea to just amplify the 60mV by 166 in one stage followed by the
buffer. Would that cause any unstabilities? In that case I may
use TL082 instead.

Shouldn't be an issue, though inputs and outputs shouldn't be routed
together. Depending on the bandwidth of your signal, you should put a
cap across the feedback resistors. It doesn't take much to kill any
chance of oscillation.

I'll keep that in mind and put a cap across each feedback resistor.
Is 10nF ok for my application?

I also have other op-amps like mc1458, lm748, lm358, lm324 and
TL071. Is TL084 a good choice in this particular circuit?

No, that's a particularly bad choice for your circuit. The input
offset voltage on that part is 20mV! That's 1/3 of your full scale
signal. Not good. You should easily be able to find something with
one or two millivolts of input offset.

You're right about this and I have found a lot of opamps with low
offset input voltage. I'll write them and do some shopping tomorrow.
But most of them are in single and dual packages. Thanks for your
good advice!

As for the power supply. I have only +24V DC from a battery.
Would the value of R1 and R2 be OK for the circuit to work?

It's going to be noisy, but it should work. You might add another
opamp in a voltage follower configuration to buffer this point. Also,
add a couple of .1uf caps (and maybe even lower values also) in
parallel with the 100uF caps. Another step would be to use this
additional opamp as an active filter for your bias network.- Hide quoted text -

I'll take care of this by putting a virtual ground circuit using one
of the opamps and connecting a few .1uF for power decoupling.

Regards,

Allen

> - Show quoted text -

Allen Bong · May 5, 2010

On May 5, 7:11 am, "George Jefferson" <phreon...@gmail.com> wrote:

"Allen Bong" <allenbsf6...@gmail.com> wrote in message

news:7041d68b-b2bf-47cb-9382-45a905c57642@34g2000prs.googlegroups.com...

Hello group,

I wish to construct a circuit to amplify an input voltage of 0 to
60mV dc to output 0 to 10V linearly.
I have came out with a simple circuit as below:

TL084
0-60mV TL084
input |\ TL084
o-o------|+\ |\
| | | >---o--------|+\ |\ 0-10V
V - +--|-/ | | >----o----------|+\ output
- ^ | |/ | +--|-/ | | >----o----o
| | | | | |/ | | +--|-/ | |
o-o | ___ | | ___ | |100K | |/ | /+\
| +--|___|--+ +---|___|--+ preset| | ( )
| | 190k | 47K +--------- + \-/
| .-. .-. |
| | | | | |
GND | |10k | |10k ==> > '-' '-' GND
| |
GND GND
----o-----o--------- +24V
Vcc op amp | |
.-. |+
R1 | | ==> > 10k | | /-\ 100uF
'-' |
| |
GND ----o-----o
| |
.-. |+
R2 | | ==> > 10K | | /-\ 100uF
'-' |
Vss op amp | |
----o-----o---------0V

(created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de)

The first op-amp amplifies the signal by 20 and the second op-amp
amplifies the output by 5-15 times. The third stage is a buffer.
The op-amp used is a TI TL084. I was wondering if it is a good
idea to just amplify the 60mV by 166 in one stage followed by the
buffer. Would that cause any unstabilities? In that case I may
use TL082 instead.

I also have other op-amps like mc1458, lm748, lm358, lm324 and
TL071. Is TL084 a good choice in this particular circuit?

As for the power supply. I have only +24V DC from a battery.
Would the value of R1 and R2 be OK for the circuit to work?

Thanks,

Allen

Why not use an instrumentation op amp configuration?

http://en.wikipedia.org/wiki/Instrumentation_amplifier

You can buy single packages that do it all for you.- Hide quoted text -

- Show quoted text -

Hi George,

Thanks for letting me know about this type of opamp. I'll take a good
look at it and see if they are available locally. Looks like MAX4194
is a good candidate. Does Maxim give away free samples?

Allen

David Eather · May 5, 2010

On 5/05/2010 8:33 AM, Allen Bong wrote:

On May 4, 9:02 pm, N0S...@daqarta.com (Bob Masta) wrote:
On Tue, 4 May 2010 00:35:32 -0700 (PDT), Allen

Bong<allenbsf6...@gmail.com> wrote:
Hello group,

I wish to construct a circuit to amplify an input voltage of 0 to
60mV dc to output 0 to 10V linearly.
I have came out with a simple circuit as below:

TL084
0-60mV TL084
input |\ TL084
o-o------|+\ |\
| | |>---o--------|+\ |\ 0-10V
V - +--|-/ | |>----o----------|+\ output
- ^ | |/ | +--|-/ | |>----o----o
| | | | | |/ | | +--|-/ | |
o-o | ___ | | ___ | |100K | |/ | /+\
| +--|___|--+ +---|___|--+ preset| | ( )
| | 190k | 47K +--------- + \-/
| .-. .-. |
| | | | | |
GND | |10k | |10k ===
'-' '-' GND
| |
GND GND
----o-----o--------- +24V
Vcc op amp | |
.-. |+
R1 | | ===
10k | | /-\ 100uF
'-' |
| |
GND ----o-----o
| |
.-. |+
R2 | | ===
10K | | /-\ 100uF
'-' |
Vss op amp | |
----o-----o---------0V

(created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de)

The first op-amp amplifies the signal by 20 and the second op-amp
amplifies the output by 5-15 times. The third stage is a buffer.
The op-amp used is a TI TL084. I was wondering if it is a good
idea to just amplify the 60mV by 166 in one stage followed by the
buffer. Would that cause any unstabilities? In that case I may
use TL082 instead.

I also have other op-amps like mc1458, lm748, lm358, lm324 and
TL071. Is TL084 a good choice in this particular circuit?

As for the power supply. I have only +24V DC from a battery.
Would the value of R1 and R2 be OK for the circuit to work?

Thanks,

Allen

A couple of points: It's not clear what your
overall goal is here, but with an overall gain of
167 you are probably going to need to be concerned
with offset voltage and drift in the op-amps.

I don't know what the final load is supposed to
be, but I presume this is for some sort of
measurement. If so, and offset and drift are
problems, you could consider a "chopper" circuit:
Extend the front fork... oops, wrong chopper!
Seriously, the way to beat offset/drift in high
gain circuits is to "chop" the input signal to
make it into a square wave, then amplify it with
AC gain stages and measure the peak-to-peak
output. Lots of options here.

Note that this approach eliminates problems due to
intrinsic op-amp offset and drift, but does
nothing for gain drift due to resistor thermal
effects, etc.

Regarding the power supply, you should consider
using one op-amp as a "ground splitter". You
should consider this whether you go with your
original cicuit, or something fancier with a
chopper. Instead of the circuit you show, use 2
equal-valued resistors (10k is OK) to divide the
24V as shown, then feed that to an op-amp buffer
that drives the "ground" for the rest of the
circuit. You probably don't need the 100uF caps
on the divider, just a single smaller cap from the
12V midpoint to the true input ground... maybe
0.1uF, just to keep noise down.

Best regards,

Bob Masta

DAQARTA v5.10
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
Frequency Counter, FREE Signal Generator
Pitch Track, Pitch-to-MIDI
DaqMusic - FREE MUSIC, Forever!
(Some assembly required)
Science (and fun!) with your sound card!- Hide quoted text -

- Show quoted text -

Hi Bob,

Thanks for your reply and recommendations. The input of the circuit
is a current sensor which outputs 60mV DC when the current is
maximum. The output of the circuit goes to a 10V volt meter. Yes it
is used for some sort of measurment.

I have googled on chopper circuit and came across this link

http://www.national.com/an/AN/AN-79.pdf

It says that a good low drift preamp like LM121 would be an
alternative for a chopper solution as you suggested. But I cant seem
to find the datasheet for LM121 even in my 1982 NS linear databook. I
would like to know the gain of this device to see if I can make use of
it.

Googling "ground splitter" finally get me to "Virtual ground
circuits"

http://tangentsoft.net/elec/vgrounds.html

I never knew that there are so many ways to do it even with
transistors. I picked the one with op-amp as you suggested.

Thanks and regards.

Allen

The LM121 has gone the way of the dodo.

Try this device -

http://www.national.com/pf/LM/LMC6084.html#Overview

LMC6084 which should get you close to what you need. It's in a PDIP or
SOIC package so you shouldn't have any trouble soldering it.

krw@att.bizzzzzzzzzzzz · May 5, 2010

On Tue, 4 May 2010 17:59:40 -0700 (PDT), Allen Bong <allenbsf6502@gmail.com>
wrote:

On May 4, 9:14 pm, "keith...@gmail.com" <keith...@gmail.com> wrote:
On May 4, 2:35 am, Allen Bong <allenbsf6...@gmail.com> wrote:

Hello group,

I wish to construct a circuit to amplify an input voltage of 0 to
60mV dc to output 0 to 10V linearly.

What is the frequency of your signal?

I have came out with a simple circuit as below:

TL084
0-60mV TL084
input |\ TL084
o-o------|+\ |\
| | | >---o--------|+\ |\ 0-10V
V - +--|-/ | | >----o----------|+\ output
- ^ | |/ | +--|-/ | | >----o----o
| | | | | |/ | | +--|-/ | |
o-o | ___ | | ___ | |100K | |/ | /+\
| +--|___|--+ +---|___|--+ preset| | ( )
| | 190k | 47K +--------- + \-/
| .-. .-. |
| | | | | |
GND | |10k | |10k ===
'-' '-' GND
| |
GND GND
----o-----o--------- +24V
Vcc op amp | |
.-. |+
R1 | | ===
10k | | /-\ 100uF
'-' |
| |
GND ----o-----o
| |
.-. |+
R2 | | ===
10K | | /-\ 100uF
'-' |
Vss op amp | |
----o-----o---------0V

(created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de)

The first op-amp amplifies the signal by 20 and the second op-amp
amplifies the output by 5-15 times. The third stage is a buffer.

*Generally* it's a good idea to put all the gain in one stage. The
only reason for not doing this is if you run into gain-bandwidth
problems with one stage.

The input signal is DC. So it's ok to amplify the signal by 167 in
one stage as it is DC.

It never changes? Well, there's no reason to monitor it then. ;-)
Seriously, it matters how fast the signal is expected to change.

The op-amp used is a TI TL084. I was wondering if it is a good
idea to just amplify the 60mV by 166 in one stage followed by the
buffer. Would that cause any unstabilities? In that case I may
use TL082 instead.

Shouldn't be an issue, though inputs and outputs shouldn't be routed
together. Depending on the bandwidth of your signal, you should put a
cap across the feedback resistors. It doesn't take much to kill any
chance of oscillation.

I'll keep that in mind and put a cap across each feedback resistor.
Is 10nF ok for my application?

Is 1600Hz operation OK? I was thinking more along the lines of 1nF or even
100pF, but it varies by application.

I also have other op-amps like mc1458, lm748, lm358, lm324 and
TL071. Is TL084 a good choice in this particular circuit?

No, that's a particularly bad choice for your circuit. The input
offset voltage on that part is 20mV! That's 1/3 of your full scale
signal. Not good. You should easily be able to find something with
one or two millivolts of input offset.

You're right about this and I have found a lot of opamps with low
offset input voltage. I'll write them and do some shopping tomorrow.
But most of them are in single and dual packages. Thanks for your
good advice!

Unless you chopper stabilize it, good idea. Add a chopper and the input
offset isn't all that important.

As for the power supply. I have only +24V DC from a battery.
Would the value of R1 and R2 be OK for the circuit to work?

It's going to be noisy, but it should work. You might add another
opamp in a voltage follower configuration to buffer this point. Also,
add a couple of .1uf caps (and maybe even lower values also) in
parallel with the 100uF caps. Another step would be to use this
additional opamp as an active filter for your bias network.- Hide quoted text -

I'll take care of this by putting a virtual ground circuit using one
of the opamps and connecting a few .1uF for power decoupling.

Virtual ground? You want a "non-inverting unity-gain", "voltage-follower", or
"buffer" configuration.

krw@att.bizzzzzzzzzzzz · May 5, 2010

On Tue, 4 May 2010 18:03:49 -0700 (PDT), Allen Bong <allenbsf6502@gmail.com>
wrote:

On May 5, 7:11 am, "George Jefferson" <phreon...@gmail.com> wrote:
"Allen Bong" <allenbsf6...@gmail.com> wrote in message

news:7041d68b-b2bf-47cb-9382-45a905c57642@34g2000prs.googlegroups.com...

Hello group,

I wish to construct a circuit to amplify an input voltage of 0 to
60mV dc to output 0 to 10V linearly.
I have came out with a simple circuit as below:

TL084
0-60mV TL084
input |\ TL084
o-o------|+\ |\
| | | >---o--------|+\ |\ 0-10V
V - +--|-/ | | >----o----------|+\ output
- ^ | |/ | +--|-/ | | >----o----o
| | | | | |/ | | +--|-/ | |
o-o | ___ | | ___ | |100K | |/ | /+\
| +--|___|--+ +---|___|--+ preset| | ( )
| | 190k | 47K +--------- + \-/
| .-. .-. |
| | | | | |
GND | |10k | |10k ===
'-' '-' GND
| |
GND GND
----o-----o--------- +24V
Vcc op amp | |
.-. |+
R1 | | ===
10k | | /-\ 100uF
'-' |
| |
GND ----o-----o
| |
.-. |+
R2 | | ===
10K | | /-\ 100uF
'-' |
Vss op amp | |
----o-----o---------0V

(created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de)

The first op-amp amplifies the signal by 20 and the second op-amp
amplifies the output by 5-15 times. The third stage is a buffer.
The op-amp used is a TI TL084. I was wondering if it is a good
idea to just amplify the 60mV by 166 in one stage followed by the
buffer. Would that cause any unstabilities? In that case I may
use TL082 instead.

I also have other op-amps like mc1458, lm748, lm358, lm324 and
TL071. Is TL084 a good choice in this particular circuit?

As for the power supply. I have only +24V DC from a battery.
Would the value of R1 and R2 be OK for the circuit to work?

Thanks,

Allen

Why not use an instrumentation op amp configuration?

http://en.wikipedia.org/wiki/Instrumentation_amplifier

You can buy single packages that do it all for you.- Hide quoted text -

- Show quoted text -

An instrumentation amp isn't going to buy anything in this application. The
input offset will likely eat him alive.

Hi George,

Thanks for letting me know about this type of opamp. I'll take a good
look at it and see if they are available locally. Looks like MAX4194
is a good candidate. Does Maxim give away free samples?

Maxim doesn't even sell parts. They do dream up some fantastic specs, though.
(That's a hint: stay *far* away from maxim. Don't even use their name,
except on stage at the Comedy Club).

George Jefferson · May 5, 2010

An instrumentation amp isn't going to buy anything in this application.
The
input offset will likely eat him alive.

Huh? instrumentation amps have very low dc offsets and are simply more ideal
op amps. It can do no worse than any other basic op amp configuration.

Allen Bong · May 5, 2010

On May 5, 11:47 am, "k...@att.bizzzzzzzzzzzz"
<k...@att.bizzzzzzzzzzzz> wrote:

On Tue, 4 May 2010 17:59:40 -0700 (PDT), Allen Bong <allenbsf6...@gmail.com
wrote:

On May 4, 9:14 pm, "keith...@gmail.com" <keith...@gmail.com> wrote:
On May 4, 2:35 am, Allen Bong <allenbsf6...@gmail.com> wrote:

Hello group,

I wish to construct a circuit to amplify an input voltage of 0 to
60mV dc to output 0 to 10V linearly.

What is the frequency of your signal?

I have came out with a simple circuit as below:

TL084
0-60mV TL084
input |\ TL084
o-o------|+\ |\
| | | >---o--------|+\ |\ 0-10V
V - +--|-/ | | >----o----------|+\ output
- ^ | |/ | +--|-/ | | >----o----o
| | | | | |/ | | +--|-/ | |
o-o | ___ | | ___ | |100K | |/ | /+\
| +--|___|--+ +---|___|--+ preset| | ( )
| | 190k | 47K +--------- + \-/
| .-. .-. |
| | | | | |
GND | |10k | |10k ==> >> > '-' '-' GND
| |
GND GND
----o-----o--------- +24V
Vcc op amp | |
.-. |+
R1 | | ==> >> > 10k | | /-\ 100uF
'-' |
| |
GND ----o-----o
| |
.-. |+
R2 | | ==> >> > 10K | | /-\ 100uF
'-' |
Vss op amp | |
----o-----o---------0V

(created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de)

The first op-amp amplifies the signal by 20 and the second op-amp
amplifies the output by 5-15 times. The third stage is a buffer.

*Generally* it's a good idea to put all the gain in one stage. The
only reason for not doing this is if you run into gain-bandwidth
problems with one stage.

The input signal is DC. So it's ok to amplify the signal by 167 in
one stage as it is DC.

It never changes? Well, there's no reason to monitor it then. ;-)
Seriously, it matters how fast the signal is expected to change.

Oops, yes it does change of course. But may be in the realm of 1 to
10 cycles per second.

The op-amp used is a TI TL084. I was wondering if it is a good
idea to just amplify the 60mV by 166 in one stage followed by the
buffer. Would that cause any unstabilities? In that case I may
use TL082 instead.

Shouldn't be an issue, though inputs and outputs shouldn't be routed
together. Depending on the bandwidth of your signal, you should put a
cap across the feedback resistors. It doesn't take much to kill any
chance of oscillation.

I'll keep that in mind and put a cap across each feedback resistor.
Is 10nF ok for my application?

Is 1600Hz operation OK? I was thinking more along the lines of 1nF or even
100pF, but it varies by application.

More likely 10 Hz or else the DC voltmeter wouldn't be able to get a
steady reading!

Allen

I also have other op-amps like mc1458, lm748, lm358, lm324 and
TL071. Is TL084 a good choice in this particular circuit?

No, that's a particularly bad choice for your circuit. The input
offset voltage on that part is 20mV! That's 1/3 of your full scale
signal. Not good. You should easily be able to find something with
one or two millivolts of input offset.

You're right about this and I have found a lot of opamps with low
offset input voltage. I'll write them and do some shopping tomorrow.
But most of them are in single and dual packages. Thanks for your
good advice!

Unless you chopper stabilize it, good idea. Add a chopper and the input
offset isn't all that important.

As for the power supply. I have only +24V DC from a battery.
Would the value of R1 and R2 be OK for the circuit to work?

It's going to be noisy, but it should work. You might add another
opamp in a voltage follower configuration to buffer this point. Also,
add a couple of .1uf caps (and maybe even lower values also) in
parallel with the 100uF caps. Another step would be to use this
additional opamp as an active filter for your bias network.- Hide quoted text -

I'll take care of this by putting a virtual ground circuit using one
of the opamps and connecting a few .1uF for power decoupling.

Virtual ground? You want a "non-inverting unity-gain", "voltage-follower", or
"buffer" configuration. - Hide quoted text -

- Show quoted text -

keithw86@gmail.com · May 5, 2010

On May 5, 12:11 am, "George Jefferson" <phreon...@gmail.com> wrote:

An instrumentation amp isn't going to buy anything in this application.
The
input offset will likely eat him alive.

Huh? instrumentation amps have very low dc offsets and are simply more ideal
op amps. It can do no worse than any other basic op amp configuration.

No, they really don't. Instrumentation amps are built using three
conventional opamps, the first two in a non-inverting configuration
(each of the two non-inverting inputs for each instrumentation amp
input) followed by a differential amp. They're useful for high
impedance differential sensing, but do not have a particularly low
input offset voltage. Of course, IOS can be trimmed and low IOS
opamps do exist (the AD8605/6/8 have an IOS of 20uV typical - 1000
times better than the opamp discussed above).

George Herold · May 5, 2010

On May 5, 9:58 am, "keith...@gmail.com" <keith...@gmail.com> wrote:

On May 5, 12:11 am, "George Jefferson" <phreon...@gmail.com> wrote:

An instrumentation amp isn't going to buy anything in this application.
The
input offset will likely eat him alive.

Huh? instrumentation amps have very low dc offsets and are simply more ideal
op amps. It can do no worse than any other basic op amp configuration.

No, they really don't. Instrumentation amps are built using three
conventional opamps, the first two in a non-inverting configuration
(each of the two non-inverting inputs for each instrumentation amp
input) followed by a differential amp. They're useful for high
impedance differential sensing, but do not have a particularly low
input offset voltage. Of course, IOS can be trimmed and low IOS
opamps do exist (the AD8605/6/8 have an IOS of 20uV typical - 1000
times better than the opamp discussed above).

Yup, Inst amps are great when you need a differential input with high
input impedance. But it's wrong to think of them as 'better' opamps.
They can't be used to make active filters, oscillators, rectifiers....
and all the other cool opamp circuits.

George H.

60mV to 10V voltage amplifier

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