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high speed full wave rectifier

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Terry Given

Jan 1, 1970
0
I've been playing with full wave rectifiers. one of the nicest designs
is the EDN idea on Jims website. but for 20MHz operation (200kHz
sawtooths) the opamp is a bit problematic - its response is all about
how the opamp comes out of saturation, even with the extra diode.

any thoughts?

Cheers
Terry
 
J

Jim Thompson

Jan 1, 1970
0
I've been playing with full wave rectifiers. one of the nicest designs
is the EDN idea on Jims website. but for 20MHz operation (200kHz
sawtooths) the opamp is a bit problematic - its response is all about
how the opamp comes out of saturation, even with the extra diode.

any thoughts?

Cheers
Terry

WHAT saturation? Are you tying to run it as single-supply? Don't ;-)

...Jim Thompson
 
T

Terry Given

Jan 1, 1970
0
Jim said:
WHAT saturation? Are you tying to run it as single-supply? Don't ;-)

...Jim Thompson

Brain engaged, mouth (OK, fingers) now in neutral - as opposed to the
other way round.

1N4148s are not, it seems, infinitely fast :)

doh.

Thanks Jim
 
J

Jim Thompson

Jan 1, 1970
0
Brain engaged, mouth (OK, fingers) now in neutral - as opposed to the
other way round.

1N4148s are not, it seems, infinitely fast :)

doh.

Thanks Jim

Nope ;-)

And it takes substantial OpAmp slew-rate at 20MHz to get good
performance.

I've only used the design up to around 1MHZ.

...Jim Thompson
 
J

John Larkin

Jan 1, 1970
0
I've been playing with full wave rectifiers. one of the nicest designs
is the EDN idea on Jims website. but for 20MHz operation (200kHz
sawtooths) the opamp is a bit problematic - its response is all about
how the opamp comes out of saturation, even with the extra diode.

any thoughts?

Cheers
Terry

Several people are now making RF detector chips, with linear or log
outputs, and bandwidths into the GHz.

John
 
T

Terry Given

Jan 1, 1970
0
Jim said:


interestingly enough, the datasheet for a schottky BAT54 has a 5ns Trr ?!

a BAT81 is pretty good though.
And it takes substantial OpAmp slew-rate at 20MHz to get good
performance.

an LM7171 does a reasonably good job. an LM6152 is terrible. and yeah,
its the slew rate all right.
I've only used the design up to around 1MHZ.

...Jim Thompson

interestingly enough, when I go for a 200kHz bipolar sawtooth, an LM6152
is almost as good single-supply as with bipolar supplies, and is not
much worse than the LM7171. But I'll stick in a bipolar supply anyway,
it'll only cost me $0.20 or so, and this is a proof-of-concept thing

the application is a crazy smps topology that puts terrible demands on a
CT (50Hz - 250kHz BW) - so bad I havent made one work well yet. HF or LF
performance, but not both.

And the current is bipolar, so a DCCT isnt really feasible - although a
current-output (eg LEM LAH-xx) DCCT can in theory drive a schottky
bridge, in practice the phase reversals cause evil R-R glitches -
probably because when all diodes are off the impedance gets very high.
no amount of snubbing or (realistic) loading really helps. a shame
really, cos it was a nice (OK, kinda nasty) idea....

when we go to an ASIC it'll get a lot easier (it becomes the chip
designers problem ;). unless we use the same french idiots who've made a
hash of the other ones. I've suggested we use a guy in Arizona, it'll
make arguments about politics that little bit more interesting :)

Cheers
Terry
 
T

Tim Williams

Jan 1, 1970
0
Terry Given said:
interestingly enough, the datasheet for a schottky BAT54 has a 5ns Trr ?!

Those ratings are kinda weird.. but I suppose it makes practical sense to
report whatever looks like it. Reverse recovery could be modelled as a big
capacitance at Vf ~= 0V, after all...

The thing that doesn't make sense to me is the schottkies that say 100ps
and some specific test (what was that called..) that doesn't exist except
perhaps in the annals of the IEEE. What good is a number when you aren't
told WTF it is!?

Tim
 
G

Genome

Jan 1, 1970
0
I've been playing with full wave rectifiers. one of the nicest designs
is the EDN idea on Jims website. but for 20MHz operation (200kHz
sawtooths) the opamp is a bit problematic - its response is all about
how the opamp comes out of saturation, even with the extra diode.

any thoughts?

Cheers
Terry

"unless we use the same french idiots who've made a
hash of the other ones"

Suck butt Nigger.

DNA
 
F

Fred Bloggs

Jan 1, 1970
0
Terry said:
Brain engaged, mouth (OK, fingers) now in neutral - as opposed to the
other way round.

1N4148s are not, it seems, infinitely fast :)

doh.

Thanks Jim

Tektronix has a patent on a technique using feedforward compensation
specifically for sawtooth rectification at high frequency...
 
T

Terry Given

Jan 1, 1970
0
Genome said:
"unless we use the same french idiots who've made a
hash of the other ones"

Suck butt Nigger.

DNA

piss off you whining pommy git
 
T

Terry Given

Jan 1, 1970
0
Genome said:
Immigrate to Australia before you call me a pommy git, Kiwi.

DNA

its the term we use, too :)

the first time I referred to myself as a Kiwi, my Murrcan friends were
bemused - was I a small hairy fruit?

Cheers
Terry
 
G

Genome

Jan 1, 1970
0
its the term we use, too :)

the first time I referred to myself as a Kiwi, my Murrcan friends were
bemused - was I a small hairy fruit?

Cheers
Terry

Right... That's enough carbon tax. Us French people are not interested
about how curly the hairs on your bollocks are. You do not have enough
Atols.

DNA
 
G

Glenn Gundlach

Jan 1, 1970
0
Terry said:
I've been playing with full wave rectifiers. one of the nicest designs
is the EDN idea on Jims website. but for 20MHz operation (200kHz
sawtooths) the opamp is a bit problematic - its response is all about
how the opamp comes out of saturation, even with the extra diode.

any thoughts?

Cheers
Terry

See bottom of page 19 of the Analog Devices AD8036 datasheet. It does
what you want within the restriction of 5 volt power supplies. Or do
you want Jim's circuit at 20MHz?

http://www.analog.com/UploadedFiles/Data_Sheets/AD8036_8037.pdf

GG
 
T

Terry Given

Jan 1, 1970
0
Genome said:
Right... That's enough carbon tax. Us French people are not interested
about how curly the hairs on your bollocks are. You do not have enough
Atols.

DNA

How do the french pick their rugby players?

they simply say "yoplait, yoplait, yoplait"


I doubt there is much left of mururoa at all.

Cheers
Terry
 
T

Terry Given

Jan 1, 1970
0
Glenn said:
See bottom of page 19 of the Analog Devices AD8036 datasheet. It does
what you want within the restriction of 5 volt power supplies. Or do
you want Jim's circuit at 20MHz?

http://www.analog.com/UploadedFiles/Data_Sheets/AD8036_8037.pdf

GG

Hi Glenn,

thanks, that was one solution I came up with when I went a-googling.
turns out I just needed to pick better diodes, and I can do it with a
variety of opamps. I'd have given my left nut for that clamp amp in 1992
though, when I designed a (not too flash) output stage for a pulse
generator I built.....

Cheers
Terry
 
G

Genome

Jan 1, 1970
0
How do the french pick their rugby players?

they simply say "yoplait, yoplait, yoplait"

I doubt there is much left of mururoa at all.

Cheers
Terry

Pah! Even without prompting he insults our rugby team. We will come
along and do carnage.
Please advise about the creation of the north or south atoll.

DNA
 
T

Terry Given

Jan 1, 1970
0
Genome said:
Pah! Even without prompting he insults our rugby team. We will come
along and do carnage.
Please advise about the creation of the north or south atoll.

DNA

it all sounded a bit fishy to me :)

Cheers
Terry
 
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