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Delay between +VCC and -VEE supplies of opamp

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afz23

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I am using power supplies which have time delay of 20ms between +VCC and -VEE to power an Opamp 8001.It is a level shifter circuit. It is used for converting a TTL signal to bi-polar signal at 3Mbps.
Is there any issue if opamp gets delayed supply and opamp o/p drives a diode based double balanced mixer.
 

Some ICs could latch up, depending on their internal constructions.

National Semiconductor had an old app note dealing precisely with this, and a simple solution. Can't exactly remember the arrangement, but it used diodes........let me see if I can find it in my very old app books.
 

Whether there's an "issue" with the op amp output
being not-as-intended is not for us to say. Slightly
more sound to speculate on problems for the op amp
itself. But not much.

This would seen to want simulation. If the outcomes
can be seen (like, for the first 2mS the output is stuck
high because the supply is really +15/0 and the op amp
can't pull within 2V of negative rail, but you call "high"
+1V and "low" -1V) then you can follow that through
component stress vs ratings and expected output vs
bogus output system level consequences).

Some systems I've done parts for, have had requirements
for supply levels checking and holding off operation
until all are within limits. This could be as simple as a
5mS timeout or as complicated as a supply supervisory
chip and software response to "power good".
 

Hi,

It is used for converting a TTL signal to bi-polar signal at 3Mbps.
* isn't a job for an analog Opamp.
* better use a comparator
* or an analog switch

Klaus
 

Is this for a differential output? or single ended driving a transformer with a tapped output to a diode bridge.
It's a single ended output, which is driving IF port of mixer.
Its mixer as a BPSK modulator, which receives carrier at LO port and gives modulated output at RF port.

- - - Updated - - -

Hi,


* isn't a job for an analog Opamp.
* better use a comparator
* or an analog switch

Klaus
I am using AD8001 as comparator.
 

Hi,

If you treat a dog as a horse...it won't become a horse.

Mistreating an Opamp as comparator doesn't make it to a comparator.
And even worse you use a current mode feedback Opamp for your circuit.
An Opamp is designed for analog output, inputs are considered to have equal voltage, output should never be saturated.
A comparator is designed for digital output, inputs may differ a lot, output usually is saturated.

But if you stay with your design, then don't be surprised if you don't get the expected results.

Klaus
 

AD8001 is more of a Video Amp with 40dB gain at 10MHz BW but limited to 1.5V input with 50 Ohm on Vin+ and 10MOhm on Vin- and 1kV/us slew rate

ABS MAX SPECs

Input Voltage (Common Mode) . . . . . . . . . . . . . . . . . . . . ±V S
Differential Input Voltage . . . . . . . . . . . . . . . . . . . . . . . ±1.2 V
 

Hi,

An Opamp is designed for analog output, inputs are considered to have equal voltage, output should never be saturated.
A comparator is designed for digital output, inputs may differ a lot, output usually is saturated.

But if you stay with your design, then don't be surprised if you don't get the expected results.

Klaus

Thanks Klaus for your comments.
Can you please suggest a comparator IC ,which can handle upto 10Mbps data rate?
 

Hi,

I don't know your exact specifications....and a forum isn't meant that others do your job.

But you can find them on your own:
About all comparator manufacturers provide interactive selection guides.
Like this: https://www.ti.com/amplifier-circuit/comparators/products.html#p83=0.0007;0.3

Or a distributor:
https://www.newark.com/w/c/semicond...arators/comparators/prl/results?st=Comparator
They need to have push pull outputs (not unusual for high speed types)

******
Or use an SPDT analog switch:
https://www.newark.com/c/semiconduc...exers/analog-switches?analog-switch-type=spdt
They need to have a dual power supply and a GND referenced logic input.

Klaus
 

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