Comparator & Amplifier ICs with High Bandwidth

Dear All,

I'm constructing a circuit which requires some comparators and amplifier with high bandwidth. What ICs should I use for bandwidth more than 10MHz? How about above 100MHz?? Is LM139 suitable for bandwidth above 10MHz? I looked at the datasheet but it did not show anything regarding bandwidth. Any comments would be very appreciated.

Regards, Will

Reply to
chickenwing2010
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They quote propogation delay for comparators, not frequency.

The LM139 has a typical response time of 1.3us - not even fast enough for 1 MHz.

I used the Analog Devices AD8561 "Ultrafast 7 ns Single Supply Comparator" for converting sine waves to TTL at 16 MHz. That's not it's maximum frequency - but it won't do 100 MHz.

Reply to
Andrew Holme

Being a comparator the LM139 datasheet doesn't have any "bandwidth" parameter specified, but it does provide a response time parameter. For a small amount of input overdrive (IE: 5mV) the LM139 will waste vaguely around 1.3us before the output transitions (slightly different for positive versus negative going output transitions, see the graphs). For large input overdrive voltages (IE: large voltage differences on the order of 100mV or more between the inverting and non-inverting inputs) the delay shrinks to something more like 300ns.

Either way, the LM139 is way too slow for applications anywhere near 10MHz. Even at 1MHz it isn't very useful.

Linear Technology makes some pretty fast comparators such as the LT1715 (around 4ns response time).

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Unfortunately fast comparators usually aren't very cheap. The LM319 offers fairly decent bang for your buck, but it has an 80ns response time.

Reply to
Fritz Schlunder

A comparator data sheet will talk about "response time" or "delay". If it's a decent data sheet it'll have a chart of delay vs. differential voltage (they're generally slower with smaller inputs).

Figuring out how the delay impacts the speed that your circuit can operate is left as an exercise to -- you.

--
Tim Wescott
Wescott Design Services
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Reply to
Tim Wescott

Hi Fred,

I'd like to apologize to you. I feel really sorry if I did anything wrong before. And thanks to those who helped me regarding my questions.

Will

Reply to
chickenwing2010

Will, Fred is our resident wacko. You would be best served by kill-filing him.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

you didn't have your Java yet this morning Fred ?

Reply to
Jamie

There are comparators and line receivers being as fast as 200ps or so available as standard products. What input voltage range and logic levels were you thinking of ? The jitter can also be specified, though there the risetime of the signal comes in. The 100MHz can be done with a MC100EL16 & MC100ELT23, above ECL, LVDS and CML become standard.

Rene

--
Ing.Buero R.Tschaggelar - http://www.ibrtses.com
& commercial newsgroups - http://www.talkto.net
Reply to
Rene Tschaggelar

Get lost!- and don't post to this newsgroup again.

Reply to
Fred Bloggs

As everybody has already said, the LM139 isn't suitable for bandwidths above 10MHz.

Comparators are usually built with several stages of gain and no frequency compensation, unlike op amps - so their gain usually stays flat out to quite high frequencies, then falls off rapidly when each of the gain stages starts running out of gain at the same frequency.

Comparator data sheets rarely specify this frequency, but the data sheet for Linear Technology "ultrafast" LT10106, which has a 10nsec propagation delay, includes an application circuit which uses it to make a crystal oscillator - specifically a 10MHz to 25MHz crystal oscillator, which suggests that it isn't much use over 25MHz.

The application notes also includes the claim that the LT1016 has a gain bandwidth product of about 50GHz, which - for a part that has a typical gain of 3000, implies a bandwidth of 17MHz.

There are faster parts around - the Honeywell, then SPT and now Fairchild SPT9689 has its 3dB point at 900MHz, but it costs $20 and Arrow Electronics list a two week delivery time.

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Maxim have parts that are cheaper, and tolerably fast

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which do seem to be able to cope with 100MHz signals - the data sheet examples are of 100MHz square waves. Newark have 175 MAX9691ESA in stock for $6.00 each.

------------ Bill Sloman, Nijmegen

Reply to
bill.sloman

Hi Fred,

Just want to say SORRY ...

Will

Reply to
chickenwing2010

Really? And who the hell do you think you're fooling? You've been doing NOTHING for the past several months but cluttering up the server with your worthless off-topic, pseudo-intellectual, ignorant crap- while producing NOTHING of any informational worth to electronics- because you know damned little about the topic. Why don't you just take a hike, disappear, die, and/or get the hell off the NG too. You won't be missed.

Reply to
Fred Bloggs

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