[hpsdr] Odyssey Siren Design

[Joseph Julicher]

very nice.
That makes complete sense and answers all the issues.  I will use  
that in Siren.


On Sep 20, 2006, at 1:10 AM, Ahti Aintila wrote:

> Hi Joseph and Lyle,
>
> Excellent ideas! Anyhow, please note that LMH6624 has a rather high
> 1/f-noise corner (10 kHz).
>
> You possibly may find also my modification of the Active Integrating
> Quadrature Sampling Detector concept interesting (ISD for short). This
> schematic is modified for +3.3V and +5V supply voltages:
> <http://kotisivu.dnainternet.net/ahti/sdr-1000/2rzisd.pdf> To increase
> the blocking range with high level signals, you may need to adjust R13
> for minimal commom mode DC-output. I have not tested this circuit, but
> here are my measurements with another circuit:
> <http://kotisivu.dnainternet.net/ahti/sdr-1000/AIQSDb.pdf>
>
> See also Ray Anderson's write-up on Phoenix pages.
>
> 73, Ahti OH2RZ
>
> On 20/09/06, Lyle Johnson <kk7p at wavecable.com> wrote:
>> ***** High Performance Software Defined Radio Discussion List *****
>>
>> > I am about 80% finished in the schematic entry on Siren and ran  
>> into an
>> > interesting design idea that may help simplify the power supply  
>> for use
>> > in portable (or extraterrestrial) designs.
>> >
>> > We are using the TI TLV320AIC31 Codec which has differential  
>> inputs and
>> > outputs.
>> > The I/Q demodulator is the standard QSD circuit.
>> > To improve the S/N ratio a good instrumentation amplifier is  
>> typically
>> > used after the QSD commutator and before the CODEC.
>> > However, there are two problems:
>> > 1) the INAMP requires a bipolar power supply, and
>> > 2) the TI CODEC has a differential input and the INAMP will  
>> convert the
>> > differential QSD signal to a single ended signal.
>> >
>> > I am proposing the following solution:
>> > Put a low noise 10x buffer on each line beween the codec and the  
>> qsd.
>> > The LMH6624 is a low noise opamp from National.  At 1MHz it has
>> > 0.92nv/sqrt(hz) noise.  That is quite low.
>> > http://www.national.com/pf/LM/LMH6624.html
>> >
>> > The + and - signals are directly fed to the CODEC.  The circuit  
>> shown
>> > provides the following transfer function.
>> >
>> > Vout = (Vin - 1.65)10 + 1.65
>>
>> It will only have an output swing of 2V (+/- 1V about the center)  
>> with a
>> single 5V supply, and each amplifier consumes 12 to 18 mA.
>>
>> A Linear Tech LT6231 is 1.1 nV-rt-Hz (at 10 kHz), stable at unity  
>> gain,
>> draws 3.5 mA/amplifier, rail-to-rail output.
>>
>> Anyway, I like the idea of a low-noise buffer to reduce the  
>> equivalent
>> noise figure of the ADC input!
>>
>> 73,
>>
>> Lyle KK7P
>>
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