[hpsdr] Odyssey Siren Design

[Ahti Aintila]

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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