Re: Frequency response of LDRs

From: Jim Thompson (thegreatone_at_example.com)
Date: 02/10/05 

Date: Thu, 10 Feb 2005 08:25:39 -0700

On Thu, 10 Feb 2005 07:20:12 -0800, "Joel Kolstad"
<JKolstad71HatesSpam@Yahoo.Com> wrote:

><bill.sloman@ieee.org> wrote in message
>news:1108032036.727058.300680@f14g2000cwb.googlegroups.com...
>> Wost case turn-on and turn-off times are listed as 25usec, but the
>> resistive element is a FET rather than some horrible lump of CdS.
>
>I was under the impression that one of the benefits of an LDR using CdS was
>that it's much, much more linear than a FET?
>
>In my case the resistance value will change very slowly (i.e., a
>microcontroller is going to set the gain of an op-amp a few times per day or
>something when someone wants a bigger/smaller signal) so I don't care how
>quickly the LDR can be 'modulated' or if there's 'history' (so long as the
>history's effect dies out within some seconds), just what the parasitics on
>the CdS part are that'll slow down the op-amp's loop response.
>
>Thanks for the help,
>---Joel
>

If it's uP-controlled, why not use a ladder of R's switched with
analog switches?

                                        ...Jim Thompson 

-- 
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

Relevant Pages

  • Re: Frequency response of LDRs
    ... > resistive element is a FET rather than some horrible lump of CdS. ... I was under the impression that one of the benefits of an LDR using CdS was ...
    (sci.electronics.design)
  • Re: Frequency response of LDRs
    ... >>I was under the impression that one of the benefits of an LDR using CdS was ... much more linear than a FET? ...
    (sci.electronics.design)
  • Re: Frequency response of LDRs
    ... >> resistive element is a FET rather than some horrible lump of CdS. ... As far as the resistance goes, CdS and CdSe parts are very fast, the ...
    (sci.electronics.design)