Driver to drive?

[Mac]

On Mon, 25 Oct 2004 08:28:01 -0600, uvcceet wrote:

I have a bit of experience in hardware design, but am not overly conversant in
analog such as Audio and Video.

I need to come up with a distribution switch for a CATV application involving
broadcast A/V and am looking for some advice or pointers on details on the
video side. I have the buffers/amps picked out, but I am not very good at the
biasing, and input/output loading to know exactly how to bias everything when
it comes to NTSC video.

I want to take a video source and distribute it to four output channels that
will be sent to commercial inserters for broadcast, so it has to be a good
quality design for obvious reasons....

I need a buffer coming on, an output buffer for each channel, and perhaps
something in between to drive the output buffers.

The audio can wait till I get a grip on the video, but I think that will be a
bit easier to work out. I have specific questions and haven't given much
information here, but what I am hoping for is someone who is better schooled
in the finer points of this kind of design, or perhaps url pointers or
books/manuals that I can get that will guide me through the selection of
biasing and loading the input and outputs.

I appreciate any help or comments.

Thanks,

John

First of all, I don't work in the A/V world. So take what I say with a
grain of salt.

But National Semiconductor (national.com), Maxim Integrated Circuits
(maxim-ic.com), Linear Technologies (linear.com), and Analog Devices
(analog.com) all make op-amps that are specifically designed to drive
75-Ohm video loads.

It seems to me that you could just take four of them and set them all up
with a gain of 2, then put a 75-Ohm resistor in series with each output
and you are done. Put a 75-ohm resistor on the common input to ground for
input termination, of course.

Like this (this is ASCII art, use courier or similar proportional font:


|\
| \ 75
IN-------+----+-----|+ \___________/\/\/\_______OUT 1
| | | / |
/ | +--|-/ |
\ | | |/ |
/ 75 | | |
\ | |_/\/\/\__|
/ | | Rf
| | |
| | /
GND | \
| / Ra
| \
| /
| |
| |
| GND
|
| |\
| | \ 75
+-----|+ \___________/\/\/\_______OUT 2
| / |
+--|-/ |
| |/ |
| |
|_/\/\/\__|
| Rf
|
/
\
/ Ra
\
/
|
|
GND

You would have two more op-amps connected exactly the same way.

You can get values for Rf and Ra from the datasheet. For some op-amps
(current feedback types) you basically have to use the recommended value
for Rf. And in your case, you want a gain of exactly 2, so Rf and Ra have
to be equal.

One example of a high performance op-amp (it may be overkill for your
application) is the lmh6702 from national.

I suspect there is something about this problem that I am not getting,
because it seems too easy to me. ;-)

--Mac

 

[Robert Monsen]

Rich Grise wrote:

Remember: Even a Vote for Pee-Wee Herman, is a Vote against Bush!

Unfortunately, it's not, its a vote you've wasted, when you could have
voted for somebody who could beat Bush, namely, Kerry.

This is an important election. Make your vote count.

--
Regards,
Robert Monsen

"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.

 

[Ken Smith]

In article <ep8rn0ldbfbs7btsv8e35sgeffdpnq3apm@4ax.com>,
John Fields <jfields@austininstruments.com> wrote:

On Tue, 26 Oct 2004 01:00:53 +0000 (UTC), kensmith@green.rahul.net
(Ken Smith) wrote:

In article <6a91ce9e.0410251531.23b8cf44@posting.google.com>,
Terry <t2hst@yahoo.com> wrote:
All,

Off a PIR motion detector I get a 24 volt output and when it detects
someone the pulse drops to zero for about 4 seconds. I want to trigger
a 555 timer to output about a 1/2 second pulse. What is the standard
way to take this long trigger and shorten it? Thanks.

Ascii art:


VCC
VCC !
! \
--- /
^ D1 \ R1
! !
------!!--+--+--+---TRIG and THR
C1 !
---
^ D2
!
GND


Warning: If the signal source has a low impedance, put a resistor in
series with C1 that is smaller than R1 but more than about 100 Ohms.

---____ ___
To TRIG only. THR and DIS are tied together and to the junction of
the timing cap and resistor to make a one-shot.

His input pulse is longer than the output pulse so, you don't need the
extra parts. The circuit I posted does this:



. . . . . . . . . . . . . . . .
**** . . . . . . . . . . . . . . +24V
. * . . . . . . . . . . . . . .
. * . . . . . . . . . . . . . . Input
. * . . . . . . . . . . . . . .
. ******************************************* 0V
. : . . . . . . . . . . . . . .
. : . . . . . . . . . . . . . .
. : . . . . . . . . . . . . . .
. : . . . . . . . . . . . . . .
. : . . . . . . . . . . . . . .
**** . . . . . . . ******************** Vcc
. * . . . . . . *. . . . . . . .
. * . . . . * . . . . . . . . .
. * . . . .* ............................ 2/3Vcc
. * . . .* .: . . . . . . . . . .
. * . .* .: . . . . . . . . . .
. * . *. . .: . . . . . . . . . . Trig and THR
. * * . . .: . . . . . . . . . .
. * *. . . .: . . . . . . . . . . 1/3Vcc
. ** . . . .: . . . . . . . . . .
. * . . . .: . . . . . . . . . . 0V
. : . . . .: . . . . . . . . . .
. : . . . .: . . . . . . . . . .
. : . . . .: . . . . . . . . . .
. ************** . . . . . . . . . . Vcc
. * . . . .* . . . . . . . . . . Q
. * . . . .* . . . . . . . . . . Output
**** . . . .****************************** 0V
--
--
kensmith@rahul.net forging knowledge

 

[legg]

On 25 Oct 2004 18:52:53 -0700, paulk880@yahoo.com (Paul K.) wrote:

Hi,

I'm working on a PSPICE simulation of a crystal oscillator using a
2N3819. So far it's working great.

I will build the circuit, but before I do, I wanted to make sure I'm
not exceeding the maximum drain-source voltage (Vds) of the
transistor. I'm putting approximately 22V across it.

However, none of the datasheets I could find listed the maximum
voltage that can be placed across a 2N3819 (from drain to source).

E.g. http://www.fairchildsemi.com/ds/2N/2N3819.pdf

Looking at a JFET tutorial however...

http://cnx.rice.edu/content/m1030/latest/

I get the impression that the drain-gate voltage is really what I
should be interested in. According to the datasheet, anything beyond
25V will exceed the device rating.

However, I'm curious though, what happens to a JFET when that voltage
rating (drain-gate) is exceeded? Does it avalanche like a MOSFET?
Would it survive?

Also, is there a reason why the drain-source parameter of a JFET is
not specified in its datasheet?

As the gate on the NJFet is negative with respect to the source, when
the fet is pinched off (or even in linear operation), the greatest
voltage stress occurs between gate and drain rather than between
source and drain.

Pinched-off drain current is seldom specified at a Vds greater than
half the rated Vgs or Vgd.

RL

 

[Fred Bloggs]

?

Tom Seim wrote:

"

Who cares - this group is about ELECTRONICS - I know Bush probably cannot
spell a word that long but that's not good enough reason to clutter up the
news server with crap

 

[Fred Bloggs]

Tom Seim wrote:

"

Who cares - this group is about ELECTRONICS - I know Bush probably cannot
spell a word that long but that's not good enough reason to clutter up the
news server with crap


Sorry about that.

Electronics seems to have been suspended until after the election,
which is less than 1 week away (THANK GOD!).

Perhaps then we can get back to something that makes sense.

Really- I don't see much of your participation in this group. What the
hell could you possibly be talking about.

 

[Fred Bloggs]

Tom Seim wrote:

Rich Grise <rich@example.net> wrote in message news:<pan.2004.10.25.06.28.04.326575@example.net>...

On Sun, 24 Oct 2004 21:18:06 -0700, Tom Seim wrote:


Rich Grise <rich@example.net> wrote in message news:<pan.2004.10.23.23.40.42.645372@example.net>...

On Sat, 23 Oct 2004 15:47:22 -0700, Tom Seim wrote:


Think Kerry is going to win? Well you can get great odds at

http://www.intrade.com/

$40 will buy you a contract that yields $100 on a Kerry victory. This is
down from $46 just a week ago.

So, how many people will get paid before they go broke?

Cheers!
Rich

Everybody. The Kerry contracts are balanced by the Bush contracts. If
Kerry wins, Kerry contract holders are paid by Bush contract holders,
and visa-versa.

Right, and what happens when the Bush people run out of money?
Or is it just like a football bet, where you pays your money, you
takes your chances?

and they're paying 10 for 4?

Where do I sign up!

Thanks,
Rich


You are covered because they have to pay for the contracts up front.
This is not a scam-it is for real. If you feel strongly that Kerry
will win then this is your opportunity to clean up.


The web site tells you how to sign up.

How much have you put on Bush?

 

[Fred Bloggs]

Tom Seim wrote:

Fred Bloggs <nospam@nospam.com> wrote in message news:<417D0FCA.9030203@nospam.com>...

Tom Seim wrote:

Rich Grise <rich@example.net> wrote in message news:<pan.2004.10.23.23.40.42.645372@example.net>...


On Sat, 23 Oct 2004 15:47:22 -0700, Tom Seim wrote:



Think Kerry is going to win? Well you can get great odds at

http://www.intrade.com/

$40 will buy you a contract that yields $100 on a Kerry victory. This is
down from $46 just a week ago.

So, how many people will get paid before they go broke?

Cheers!
Rich


Everybody. The Kerry contracts are balanced by the Bush contracts. If
Kerry wins, Kerry contract holders are paid by Bush contract holders,
and visa-versa.

"visa-versa"? How damned dumb are you? Oh I see- you have writing about
10 sentences of your garbage, so you're tired. You tire easily don't
you? That's because you are a lazy welfare fraud who hasn't worked even
a two hour day for the past 40 years.


I see you aren't willing to back up your bullshit with cold hard cash
(what else is new!). Guess you are STILL UNEMPLOYED!

What gives you that idea, fairy boy? Why is employment so much on your
mind? Is it that you know when the Feds shut your boondoggle down it
will be over for you. You have no salable skills- you are a freeloader.
Hmmm- and how come you don't mention too much about what you actually
do- guess freeloading is not something most freeloaders brag about, now
is it.

 

[Fred Bloggs]

Tom Seim wrote:

Fred Bloggs <nospam@nospam.com> wrote in message news:<417D10E6.6060503@nospam.com>...

Tom Seim wrote:

rolavine@aol.com (Rolavine) wrote in message news:<20041024033822.18077.00005777@mb-m03.aol.com>...
...


That sounds worse to me. However, all Bush voters should be yelled at, though
it seems unlikely anything less than use of hammers would have any effect on
their thick skulls!

Rocky


Thanks for proving my case, Rocky.

You haven't stated a case since you started posting here- you're just a
smug little phony wannabe bs artist, and you are just another alienated
freak in your home state.


The case if obvious to anyone with an IQ better than 50 - OH, guess
that leaves you out, fredfraud!

Man- you don't fool anybody- you're the most simple minded thing around.

 

[Rich Grise]

On Mon, 25 Oct 2004 19:49:21 -0700, Junaid Uppal wrote:

I actually need to implement *any* division algorithm for an input of
4bit binary numbers and yes i can use shift registers , counters and
all of them but not eproms and stuff. So do you have any pointer to
that , i am sorry,i've been trying a lot to look around , figure out
and implement a circuitory but wasnt successful at all even after
looking at books!

Well, you can achieve the same effect as an eprom look-up table with
some logic chips.

Are you allowed to use diode logic? Tell 'em you're going _really_
retro - then cheat.

Unfold a ROM.

Figuring out how do do this will add much more to your reasoning
power than having it shown to you.

There are two, four-bit inputs - how many possible sets of input
states are there? Could you translate each of these product terms
to a quotient and remainder with a few gating diodes?

You _do_ know how to build a diode AND gate, don't you? ;-)

Have Fun!
Rich

 

[Rich Grise]

On Mon, 25 Oct 2004 20:04:30 -0700, Tom Seim wrote:

Rich Grise <rich@example.net> wrote in message news:<pan.2004.10.25.03.42.01.196208@example.net>...
On Sun, 24 Oct 2004 19:41:07 -0700, Tom Seim wrote:
....
Actually people are very interested in voluntary RFID implantation.
Consider going into the hospital for surgery and getting an
incompatible anesthetic. This can be prevented by having an RFID chip
then encodes your unique identity that could, then, be referenced to
your medical records.


Fuck, man!

I didn't know you are gay.

I didn't know you cared.

These people seem to _want_ Bigh Brother!
Mabye we're in more trouble than we thought.

Yes they do. Of course, you guys know what's best for them.

I don't follow here. Who is "you guys?" And who is "them?"
And, assuming that you (Tom Seim) mean you and others in "they do,"
which others are these, who want to be ordered which toilet paper
to use, and when?

And what happens when Big Brother dictates a brand of toilet paper
that you don't like, or worse, you have to shit sometime that's not
on Big Brother's toilet paper schedule?

Think these things through to the logical conclusion, man.

Unless you are already ahriman, of course. In which case, begone!

Thanks,
Rich

 

[Rich Grise]

On Mon, 25 Oct 2004 20:36:37 -0700, Tom Seim wrote:

You are covered because they have to pay for the contracts up front.
This is not a scam-it is for real. If you feel strongly that Kerry
will win then this is your opportunity to clean up.


The web site tells you how to sign up.

Well, we all might as well, because if Adolph^H^H^H^H^H^HGeorge wins,
American money will soon become valueless anyway.

Good Luck!
Rich

 

[Leon Heller]

"Paul K." <paulk880@yahoo.com> wrote in message
news:82b10380.0410251752.bac1f5f@posting.google.com...

Hi,

I'm working on a PSPICE simulation of a crystal oscillator using a
2N3819. So far it's working great.

I will build the circuit, but before I do, I wanted to make sure I'm
not exceeding the maximum drain-source voltage (Vds) of the
transistor. I'm putting approximately 22V across it.

However, none of the datasheets I could find listed the maximum
voltage that can be placed across a 2N3819 (from drain to source).

E.g. http://www.fairchildsemi.com/ds/2N/2N3819.pdf

Looking at a JFET tutorial however...

http://cnx.rice.edu/content/m1030/latest/

I get the impression that the drain-gate voltage is really what I
should be interested in. According to the datasheet, anything beyond
25V will exceed the device rating.

However, I'm curious though, what happens to a JFET when that voltage
rating (drain-gate) is exceeded? Does it avalanche like a MOSFET?
Would it survive?

Also, is there a reason why the drain-source parameter of a JFET is
not specified in its datasheet?

Probably because the drain-source connection is basically a resistor.

Leon

 

[Ken Smith]

In article <clkb7b$2m45$1@news.iquest.net>,
John S. Dyson <toor@iquest.net> wrote:

In article <clk1oe$pjc$1@blue.rahul.net>,
kensmith@green.rahul.net (Ken Smith) writes:
In article <clitko$2796$3@news.iquest.net>,
John S. Dyson <toor@iquest.net> wrote:
[...]
Remember: the intelligence agencies from ALL OVER THE WORLD were
giving input that Saddam was planning this, planning that, etc.

It is the same folks that promiced us WMDs in Iraq that are telling us
that.

Yes, like Mr Putin made such a claim (Saddam was readying a terror
attack.) It wasn't just Bush.

Putin does have his own political axes but yes he has been seen to make
such claims.

The CIA has been weak since the Church commission in 1975, and made much
weaker in 1995 by getting rid of almost all HUMINT capability. HUMINT
has been EVEN MORE critical since the fall of the Soviets.

Why would HUMINT be EVEN MORE critical with the main enemy gone?

Please refer to the attacks against GOP headquarters over the last few
weeks.

Yup. Including gun shots. I didn't find anyone charged or any suggestion
that it was organized by the democratic party. Do you know of any?


--
--
kensmith@rahul.net forging knowledge

 

[Rich Grise]

On Tue, 26 Oct 2004 02:10:11 +0000, Fred Bloggs wrote:

Rich Grise wrote:
On Mon, 25 Oct 2004 19:41:45 +0000, Electric dabbler wrote:

Who cares - this group is about ELECTRONICS - I know Bush probably cannot
spell a word that long but that's not good enough reason to clutter up the
news server with crap


So, surely you'll tell us what _is_ a good enough reason to not only
clutter up the news server with crap, but to clutter up the news server
with old, used crap, requoting the very post he's bitching about?

Asshole.


Much better to have " Me I want good cerkyut LED plan. Pleez send now.
TIA, Klesh"

PIMP!![0]

Thanks,
Rich
[0] (that's the ROFLMAO kind...)

 

[CFoley1064]

Subject: Peak detector design resources
From: hemantsadhwani@gmail.com (hemant)
Date: 10/25/2004 11:12 PM Central Daylight Time
Message-id: <5ef22a9f.0410252012.12c8d1ce@posting.google.com

Hi,

Can anyone help me designing peak detector for signal ranging from 0 - 5
v.

Regards
Hemant

Hello. Have you looked at National Semiconductor AN-31, Op Amp Circuit
Collection, p.18?

http://www.national.com/an/AN/AN-31.pdf

About the only negative is that you'll need one -- you have to use bipolar
supplies.

Chris

 

[Brian]

"Clarence" <no@No.com> wrote in message
news:MMedd.32497$QJ3.8774@newssvr21.news.prodigy.com...

"Mike Page" <mike@SCRUBeclectic-CAPSweb.BLAMEco.SWENuk> wrote in message
news:WN2dnTVmLuuN7-jcRVnyjg@eclipse.net.uk...
Hassan wrote:
Hello;
I want to design a switching power supply with:
Vin=24 Vdc and Vo=15V @ 7A

I suggest you start with a 24V -> 12V switcher (available at 10A for
vehicular use) and "adjust" it.

Best regards,
Mike.

Possible to use:

http://www.mpja.com/productview.asp?product=14335+PS

Heavy duty.

Not a complete power supply, but an IC.
Thanks,
Brian

 

[Robert Monsen]

Ken Smith wrote:

In article <clkb7b$2m45$1@news.iquest.net>,
John S. Dyson <toor@iquest.net> wrote:

Please refer to the attacks against GOP headquarters over the last few
weeks.


Yup. Including gun shots. I didn't find anyone charged or any suggestion
that it was organized by the democratic party. Do you know of any?

Dyson says this was probably all arranged by the DNC, with 'the nod'
from Kerry himself. Remember, you heard it here first!

According to the only story I could find (not counting the rw bloggers,
many of whom appear to have the same cognitive deficit as Dyson) there
was a bank robbery across the street when cops were investigating the
incident!

http://www.wbir.com/news/news.aspx?storyid=20241

Sounds like a nice neighborhood...

Hardly fuel for conspiricy theorists, unless they are lacking in common
sense, or have a political axe to grind and hope others won't check up
on the facts.

--
Regards,
Robert Monsen

"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.

 

[Pooh Bear]

Ian Stirling wrote:

Steve <me@privacy.net> wrote:
Hi,

During EMC testing (for CE) of our product, the single output data line
failed the radiated emissions test. It is a digital audio square wave - 0.5V
pk-pk at 12.28MHz - and at 100MHz or so the emissions were just over the
allowed limit.
snip
I'm thinking that we could put pads on for a 0805 ferrite bead, and then
take the board for EMC testing with a bunch of alternative spec beads so we
can try them out while we are there. But is this likely to be successful, or
is there a better way?

Have you taken any measures to limit the slew-rate of the digital audio
signal?
Even a simple R-C filter might be helpful.

I'll second that.

A simple RC network is a very inexpensive way of controlling emissions.


Graham

 

[Pooh Bear]

Steve wrote:

"Ian Stirling" <root@mauve.demon.co.uk> wrote in message
news:417d0686$0$43607$ed2e19e4@ptn-nntp-reader04.plus.net...
Steve <me@privacy.net> wrote:
Hi,

During EMC testing (for CE) of our product, the single output data line
failed the radiated emissions test. It is a digital audio square wave -
0.5V
pk-pk at 12.28MHz - and at 100MHz or so the emissions were just over the
allowed limit.
snip
I'm thinking that we could put pads on for a 0805 ferrite bead, and then
take the board for EMC testing with a bunch of alternative spec beads so
we
can try them out while we are there. But is this likely to be
successful, or
is there a better way?

Have you taken any measures to limit the slew-rate of the digital audio
signal?
Even a simple R-C filter might be helpful.

Hi Ian,

Thanks for your suggestion. TBH we've dismissed that approach in the past
since a decreased slew rate could increase jitter on the signal. Jitter is a
problem to audiophiles (real or perceived), so limiting the slew-rate is not
something we want to do if we can at all help it.

It's a classic case of Errrrr But !

Whatever the ferrite does will have pretty much the same effect as an RC !
Otherwise it wouldn't pass the EMC test.

You really shouldn't have a problem with a dig AES ? out btw if proper screening
and earth return is applied.


Graham