Re: CMOS analogues switch capacitance

On Sat, 14 Oct 2006 11:28:57 -0400, John Popelish <jpopelish@xxxxxxxx>
wrote:

Joe G (Home) wrote:
Hi All,

I am measuring capacitance in the pF range and I need to switch monitoring
inputs.

We can calibrate out any constant capacitance.. However

The 64,000 dollar question is would you expect the input capacitances of the
CMOS switch to be constant over tempreature?

The devices I have looked at are the better versions of the CMOS 4053 etc
... a few from NXP (formerly Philips)
http://www.standardics.nxp.com/products/switches/


While there are input capacitance specifications..... there is no spec on
the relationship between input capacitance vs Temp.


Would you expect input capacitance to be fairly constant over the operating
temp range?

The short answer is that, unless someone has taken great
pains to suppress it, everything changes with temperature.

I would use an extra section of switch to measure the
capacitance of a switch, and subtract the changes of that
that from all the other measurements.

John, _Very_good_suggestion_!

The only relatively constant term would be gate capacitance, ESD and
MOS body diode capacitances will be all over the place with
temperature.

...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: Switching tiny small capacitors to a VCO
    ... on this pin" approach to set the center frequency. ... How do you switch in something so small as a 2pF cap? ... lower the off capacitance, of course. ...
    (sci.electronics.design)
  • Re: Switching tiny small capacitors to a VCO
    ... on this pin" approach to set the center frequency. ... How do you switch in something so small as a 2pF cap? ... lower the off capacitance, of course. ...
    (sci.electronics.design)
  • Re: Problem no. 1
    ... we can construct a switch that pulls apart very quickly ... There is no substance that is a perfect insulator, ... the circuit is unrealizable in a practical ... Incidentally, someone mentioned capacitance as being a factor, ...
    (sci.physics)
  • Re: CMOS analogues switch capacitance
    ... I am measuring capacitance in the pF range and I need to switch monitoring ... We can calibrate out any constant capacitance.. ... CMOS switch to be constant over tempreature? ...
    (sci.electronics.design)
  • Re: Inexpensive wide-range variable capacitor?
    ... > could set any capacitance in the range to within 3 pF. ... > shunts to switch each cap. ... become significant circuit components. ...
    (sci.electronics.basics)
Quantcast