OpAmp Input Stage with different voltage ranges

[Marco T.]

Hallo,
I must develop a system that should accept at the input the following
voltage ranges:

0 5v
0 10v
0 15v

I thought two chances:

1) Using a voltage divider where I could choose the couple of resistor using
2 multiplexer.
I connect every resistor to input of a mux and I configure the two mux using
a couple of jumpers.
Then I connect to oupt of voltage divider a opamp voltage follower or
similar.

2) Using a programmable gain amplifier.

There are orther chances?

Any comments is very appreciated.

Many Thanks
Marco

 

[Marco T.]

Hallo,
I must develop a system that should accept at the input the following
voltage ranges:

0 5v
0 10v
0 15v

I thought two chances:

1) Using a voltage divider where I could choose the couple of resistor
using 2 multiplexer.
I connect every resistor to input of a mux and I configure the two mux
using a couple of jumpers.
Then I connect to oupt of voltage divider a opamp voltage follower or
similar.

2) Using a programmable gain amplifier.

There are orther chances?

Any comments is very appreciated.

Many Thanks
Marco

I forgotten to say that output stage must be in range 0 5v.

 

[mmm]

If you want to use jumpers to configure the mux just remove the mux and
use jumpers to configure input topology ( or even place only needed
resistors )

input
o---R----o---o------ to OPAmp
| |
R R
| |
GND GND to ground trough jumpers

leave jumpers open for 0-5 range put one jumper for 0-10 two jumpers for
0-15 range

input impedance change on different range

max134 from maxim show an interesting topology for input range selector

 

[Spehro Pefhany]

Hallo,
I must develop a system that should accept at the input the following
voltage ranges:

0 5v
0 10v
0 15v

I thought two chances:

1) Using a voltage divider where I could choose the couple of resistor using
2 multiplexer.
I connect every resistor to input of a mux and I configure the two mux using
a couple of jumpers.
Then I connect to oupt of voltage divider a opamp voltage follower or
similar.

2) Using a programmable gain amplifier.

There are orther chances?

Any comments is very appreciated.

Many Thanks
Marco

If you're using an ADC you could consider use more resolution than you
need and throw away an LSB or two for the lower voltage inputs.

If you don't mind using jumper blocks, this is pretty easy/cheap:


In Jumper position
o 1: 0~15V
| 2: 0~10V
.-. 3: 0~5V (storage position for jumper block)
20K0 | |
| |
'-'
|
1 | 2 3
.--|--------. Out
| o--o--o----------------o
| |
| o o o |
'--|--|-----'
.-..-.
| || |
| || |
10K0 '-''-'20K0
| |
| |
======
GND

You can buffer the input and/or output if you like.



Best regards,
Spehro Pefhany

 

[David L. Jones]

Hallo,
I must develop a system that should accept at the input the following
voltage ranges:

0 5v
0 10v
0 15v

I thought two chances:

1) Using a voltage divider where I could choose the couple of resistor using
2 multiplexer.
I connect every resistor to input of a mux and I configure the two mux using
a couple of jumpers.
Then I connect to oupt of voltage divider a opamp voltage follower or
similar.

2) Using a programmable gain amplifier.

There are orther chances?

Any comments is very appreciated.

Many Thanks
Marco

If you have a high input impedance and minimum settling time is
important then you might be better off having a seperate resistor
divider and buffer for each input and then have the mux on the low
impedance output of the buffers.

One fixed divider plus a programmable gain amp is probably the simplest
solution though.

Or simply a fixed 15V range and a higher res ADC as someone else
mentioned.

I think Maxim make ADCs with built-in selectable ranges like this.

Dave

 

[jasen]

On Thu, 27 Jul 2006 10:29:33 +0200, the renowned "Marco T."

If you don't mind using jumper blocks, this is pretty easy/cheap:


In Jumper position
o 1: 0~15V
| 2: 0~10V
.-. 3: 0~5V (storage position for jumper block)
20K0 | |
| |
'-'
|
1 | 2 3
.--|--------. Out
| o--o--o----------------o
| |
| o o o |
'--|--|-----'
.-..-.
| || |
| || |
10K0 '-''-'20K0
| |
| |
======
GND

The third position isn't needed the jumper can be stored horizontaly

Bye.
Jasen