[hpsdr] Odyssey Siren Design

[Steven Bible]

Hello Ahti,

Joe and I have been studying your circuit for Project Odyssey.  I have a
couple of questions:

1. What criteria did you use in selecting the OPA1632?  I've been reading
the app notes that you recommended, and out of curiousity, searched the TI
web site for full differential op amps to see what else is available.  I was
surprised that TI's parametric search did not mention the OPA1632.  There
were many THS4xxx devices that popped up.  I am sure that low noise is a
major criteria.  I did not see any of the THS4xxx devices have any better
noise than the OPA1632.  I was a little concerned that the OPA1632 was an
expensive part (Digi-Key $3.94 qty 1), but when I saw the prices of the
THS4xxx devices, it suddenly because less expensive :-)

2. I was studying the data sheet for the SN74AUC2G53.  I noted that the Vcc
is to be 2.7V, but your schematic shows you are powering it at 3.3V? (the
absolute maximum is 3.6V).  2.7V is not a problem I think for this circuit,
but wanted to know your comments.  I also found the SN74LVC2G53 can work at
higher voltage if needed.  I have not compared the data sheets yet.  I also
found that sourcing the SN74AUC2G53 to be a little more difficult than the
SN74LVC2G53.

3. I am a little concern with using two separate muxes and the possible
clock skew between them.  I am sure that using two separate devices makes
the PCB layout easier.  But I was thinking of using the SN74CB3Q33253 that
was mentioned on the list (or was it the SoftRock40 list) to minimize my
thinking of clock skew, but I wanted to get your thoughts.

Thank you very much for sharing your circuit.  We hope to have it built in a
couple of weeks for testing for Project Odyssey.

73,

- Steve, N7HPR
 (n7hpr at tapr.org)




> -----Original Message-----
> From: hpsdr-bounces at hpsdr.org [mailto:hpsdr-bounces at hpsdr.org]On Behalf
> Of Ahti Aintila
> Sent: Thursday, September 21, 2006 1:30 AM
> To: Joseph Julicher
> Cc: hpsdr at hpsdr.org
> Subject: Re: [hpsdr] Odyssey Siren Design
>
>
> ***** High Performance Software Defined Radio Discussion List *****
>
> Joe,
>
> The bias arrangement of the opamp OPA1632 may not be the best
> regarding the power consumption. Due to the difference between the
> reference voltages of the signal switches and the opamps there will be
> some extra current drawn, if Vcom is forced to 2.5V. For safety, I
> recommend the common reference voltage 1.65V as corrected in the
> version "b": <http://kotisivu.dnainternet.net/ahti/sdr-1000/2rzisd-b.pdf>
>
> 73, Ahti OH2RZ
>
> On 20/09/06, Joseph Julicher <n9wxu at mac.com> wrote:
> > very nice.
> > That makes complete sense and answers all the issues.  I will use
> > that in Siren.
> >
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