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From: Jim Thompson on 19 Oct 2006 12:37
On Thu, 19 Oct 2006 16:34:42 GMT, Joerg
<notthisjoergsch(a)removethispacbell.net> wrote:

>Hello Joseph,
>
>>
>> There is another issue with CMOS switches operating in low noise or high
>> speed applications. It is not really like capacitance but produces similar
>> effects, it is charge injection. Charge injection is relatively free of
>> temperature effects, but varies some with input voltage and supply voltage.
>> Have you had to design to control it?
>>
>
>I guess anybody who ever designed samplers has. It's not always fun
>though, especially when you find out like I did a few years ago that
>your favorite quad array has been priced out of the typical BOM budget
>range :-(
>
>However, there is another architecture that seems to not be taught
>anymore at the colleges: Four fast diodes and a toroid transformer.
>Ideally a quad but many of those have become expensive/unobtainium so I
>usually try to get away with pairs. That reduces Ci effects down to
>almost zilch.

Hard to integrate though ;-)

...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.
From: Joerg on 19 Oct 2006 13:36
Hello Jim,

>>
>>>There is another issue with CMOS switches operating in low noise or high
>>>speed applications. It is not really like capacitance but produces similar
>>>effects, it is charge injection. Charge injection is relatively free of
>>>temperature effects, but varies some with input voltage and supply voltage.
>>>Have you had to design to control it?
>>>
>>
>>I guess anybody who ever designed samplers has. It's not always fun
>>though, especially when you find out like I did a few years ago that
>>your favorite quad array has been priced out of the typical BOM budget
>>range :-(
>>
>>However, there is another architecture that seems to not be taught
>>anymore at the colleges: Four fast diodes and a toroid transformer.
>>Ideally a quad but many of those have become expensive/unobtainium so I
>>usually try to get away with pairs. That reduces Ci effects down to
>>almost zilch.
>
>
> Hard to integrate though ;-)
>

Yes, even hard to buy. Making the transformer is an art, almost like
tuning a vintage Alfa Romeo (oh, only Giuseppe can do that...). They are
tiny and the wires have to be arranged just so, then push them with a
tooth pick until you see the notch on the scope right there, then pot it
up. But the performance of such samplers is astounding.

--
Regards, Joerg

http://www.analogconsultants.com
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