Re: Capacitor Discharging with CMOS Gate

On Mon, 25 Feb 2008 12:42:56 -0500, Fred Bloggs <nospam@xxxxxxxxxx>
wrote:



Fred Bloggs wrote:


Joerg wrote:

Fred Bloggs wrote:



John Larkin wrote:
> On Mon, 25 Feb 2008 08:15:16 -0500, Fred Bloggs <nospam@xxxxxxxxxx>
> wrote:
>
>
>>
>> John Larkin wrote:
>>
>>> On Sat, 23 Feb 2008 10:11:50 -0500, Fred Bloggs
>>> <nospam@xxxxxxxxxx> wrote:
>>>
>>>
>>>
>>>> John Larkin wrote:
>>>>
>>>>
>>>>
>>>>> Recently, one of my better customers started blowing up Tiny
>>>>> Logic tristate buffers that can gate a clock out to a
>>>>> connector on one of our VME modules. They never enable the
>>>>> output function, and only apply +3 dBm RF to the connector as
>>>>> an input, so we can't imagine how the chips fry. You can tell
>>>>> the dead ones by the tiny bubble of charred conformal coating
>>>>> on top the SOT-23 package. We tried every sort of abuse we
>>>>> can imagine and can't zap them here. After a zillion meetings
>>>>> and conference calls, we decided to remove the chip.
>>>>>
>>>>
>>>> Are you saying these buffers are off a bidirectional port on
>>>> your module and the customer is applying a 3dBm clock to it?
>>>> How is this terminated for input mode drive?
>>>
>>>
>>> Bandpass filter and comparator, as noted elsewhere.
>>
>> Oooooh yeah- almost guaranteed to blow the sig gen...
>>
>
>
>
> Yeah, not many sig gens can handle a load like this...
>
>
> in (o)------------470r-----+-------+---------comp+ |
> | | gnd | | +---comp- L C
> | | | | | | gnd | | gnd gnd
>
>
> Terrifying, just terrifying.
>
>
> John
>
>
Is that 470R or 47R, either way, I know of at least one fairly popular
lab grade type that would not like that at all...you should have used
a constant impedance filter. See the tutorial in US6608536, know-it-all.


Then ditch it and get a real signal generator :-)


The best damned RF generators anywhere are Rohde & Schwartz, it's the
programmable video grade jobs that act up...


I take that back, any RF gen with reasonably precise ALC will not like
JL's circuit, usually they just passively shut-down.

So they shut down when open-circuited, or when plugged into a high-Z
scope input? I've never seen any generator do that.

Once they shut down, how do they ever recover?

John


.

Relevant Pages

  • Re: Capacitor Discharging with CMOS Gate
    ... Fred Bloggs wrote: ... >> John Larkin wrote: ... lab grade type that would not like that at all...you should have used a constant impedance filter. ... The only RS generator I have here is the old SMF RF generator. ...
    (sci.electronics.design)
  • Re: Capacitor Discharging with CMOS Gate
    ... >> John Larkin wrote: ... >>> Bandpass filter and comparator, ... > Terrifying, just terrifying. ... lab grade type that would not like that at all...you should have used a constant impedance filter. ...
    (sci.electronics.design)
  • Re: Capacitor Discharging with CMOS Gate
    ... >> John Larkin wrote: ... >>> Bandpass filter and comparator, ... > Terrifying, just terrifying. ... lab grade type that would not like that at all...you should have used a constant impedance filter. ...
    (sci.electronics.design)
  • Re: Crystal drift
    ... John Larkin wrote: ... >>make a very slow very low noise sweep generator with a very narrow range ... Sideband locking is a possible strategy here. ... e.g. a 4046--it won't lock up to the image ...
    (sci.electronics.design)
  • Re: Capacitor Discharging with CMOS Gate
    ... >> John Larkin wrote: ... >>> Bandpass filter and comparator, ... not many sig gens can handle a load like this... ... > Terrifying, just terrifying. ...
    (sci.electronics.design)