there is a current mode feedback device [which does not follows the gain
bandwidth product role ] and has 1000V/usec rise time 92dB THD at 30MHz
3nV/rtHz noise, see here http://www.ti.com/lit/ds/symlink/ths4271.pdf, I
used it as a medical color Doppler application
Guanella's choke and Guanellas balun are two different animals, the
balun has a cross DC path, the choke does not have, it's other name is
1:1 transmission line transformer, in conjunction with an A/D converter
the choke has the function to prevent a current path to the ground via
one of the the differential inputs, also used in high dynamic range
medical ultrasound application
73
Alex
On 8/21/2016 1:29 PM, Attila Kinali wrote:
On Sun, 21 Aug 2016 10:04:10 -0700
Alex Pummer <a...@pcscons.com> wrote:
directional coupler/circulator could be made with high bandwidth [ up to
1GHz ] operational amplifiers, that circulator will work from DC..
While this is a valid option, it would then become the element in the
system that limits dynamic range. It's better to use a "noiseless"
passive circuit that has very little distortion.
Also keep in mind that even if the opamp has an GBW of 1GHz or more,
the slewrate kicks in quite early and in this case would limit the
maximum signal strength severely. There is a reason why GHz amplifiers
use so much power.
driving A/D converter input asymmetrically; drive trough a
Guanella-choke, but match the output of the choke
The Guanella balun, like all other transformer based baluns,
has the same upper and lower frequency limits: The inductance
sets the lower limit (more inductance -> lower frequency) and
the loss in the ferrite sets the upper limit (non-linear and thus
can be quite abrupt). Another issue here is symmetry of output
over frequency (c.f. [1]). I don't know how good the Guanella
baluns are in reality, but this is definitly something that should
be looked at.
Attila Kinali
[1]
http://www.markimicrowave.com/blog/2013/07/why-buy-a-high-quality-baluntransformer-for-an-analog-to-digital-converter-adc/
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