Voltage Divider

[Rich Grise]

On Jan 26, 1:14 pm, dbvanhorn <[email protected]> wrote:

It's hard to ask for something precisely when you don't yet know what
the name of it is..

So thanks for the helpful replies, but I think I'll pass on the
"attitude" replies.

http://www.analog.com/UploadedFiles/Data_Sheets/AD633.pdf
Page 5, fig. 7.

Hope This Helps!
Rich

 

[JosephKK]

Right, I don't have that one handy, but I have found some examples in
NS app notes.


Monopulse resolution enhancement.

Think of two sensors, could be phototransistors, CdS cells, etc
looking out with their detection fields overlapping.
If you plot the response of either, you get a broad hump.
If you sum them, you get a broader hump with a dip in the middle, but
still indistinct.
Difference is similarly unhelpful.
But if you sum them, and divide that by the absolute value of the
difference, you get a very sharp peak.

OK. You want a true analog divide, thus the answer is related to the
log+antilog solutions already posted. There are IC's that perform
(X*Y)/10Z available (-10 V - 0 V - +10 V; full sphere/cube and half
sphere/cube). Perhaps one of these would make your design
faster/easier.

 

[JosephKK]

Neat part.

 

[JosephKK]

It may not be what is normally thought of when the expression "voltage
divider" is encountered, but by normal language usage, something that
divides one voltage by a nother is reasonably called a voltage divider.

Sylvia.

It can be but normally is not, the most common term is analog divider
for historical reasons relating to analog multipliers (Gilbert cell).

 

[JosephKK]

That's actually a voltage multiplier with scaled factors.

Graham

Divide is the inverse of multiply; not a scale factor.

 

[Sylvia Else]

Moreover, the multiplication of that result by 1V would yield the same
result as if it hadn't been multiplied at all.

The result of dividing one voltage by another is a dimensionless value,
which is incapable of being represented by the output from an analogue
system. So it has to be multiplied by something, which becomes the unit
in which the result is expressed. In this particular case, multiplying
it by 1V makes the result fit the OP's example.

Sylvia.

 

[Jasen Betts]

Right, I don't have that one handy, but I have found some examples in
NS app notes.


Monopulse resolution enhancement.

Think of two sensors, could be phototransistors, CdS cells, etc
looking out with their detection fields overlapping.
If you plot the response of either, you get a broad hump.
If you sum them, you get a broader hump with a dip in the middle, but
still indistinct.
Difference is similarly unhelpful.

try abs(a-b)

But if you sum them, and divide that by the absolute value of the
difference, you get a very sharp peak.

indeed, a peak that sharp is called an asymptote.

a+b
-----
|a-b|

will be hard to do in analogue, especially as you're interested in the
high bit.

a+b

 

[JosephKK]

The result of dividing one voltage by another is a dimensionless value,
which is incapable of being represented by the output from an analogue
system. So it has to be multiplied by something, which becomes the unit
in which the result is expressed. In this particular case, multiplying
it by 1V makes the result fit the OP's example.

Sylvia.

Nutcase, we are talking about physical circuits here. Maintain
context. Silly dimensional analysis means nothing to the circuits
involved.

-10 points.

 

[Eeyore]

That's actually a voltage multiplier with scaled factors.

On further contemplation it seems you're right.

So why does no-one make a voltage divider chip ?

Graham

 

[Eeyore]

You're wrong.

Isn't that what you always say ?

Graham

 

[Mark Zenier]

Wrong book. Try Jung's _IC OP-Amp Cookbook_.

Wow.. So much argument over terminology.
FWIW I'm no "beginner". I know what I'm after is NOT a resistive
divider, and I didn't want to fend off 1000 replies telling me to use
two resistors.
That's why I included the part illustrating that what I wanted was the
division of voltage A by voltage B, and not the division of voltage A
by some constant.

The end result is a circuit to do monopulse resolution enhancement of
two sensors with overlapping detection fields.

The circuit needs to take two inputs, A and B, and give the result of
(A+B)/abs(A-B)
I had everything worked out at that point except for the analog
divider.

I've found several approaches using log-antilog now, and I'm satisfied
with that at this point.
I didn't know what to call it when I asked, as I'd not seen such a
circuit in quite some time, and looking thru H+H I also came up blank.
It's hard to ask for something precisely when you don't yet know what
the name of it is..

So thanks for the helpful replies, but I think I'll pass on the
"attitude" replies.

Another way, especially if you need digital numbers in there somewhere, is
to use the analog and reference inputs of a succesive approximation ADC.
Make sure the reference input can handle the AC response, some chips
stick some strange slow op-amps in there internally.

Mark Zenier [email protected]
Googleproofaddress(account:mzenier provider:eskimo domain:com)