LM565 / LM567 Questions

[MrAureliusR]

Good day everyone! I haven't been on here in a while because my new job and hobbies are taking up more of my time. Still spend hours at the bench every day, though.

Just a quick question for those out there who have used these two chips: I'm looking at using either one in a design. They will be decoding FSK (which, incidentally, is one of the example circuits in the LM565 datasheet).

Two questions -- first of all, the example circuit shows the output of the LM565 going to an LM111, which is very obsolete... what would be a comparable comparator? I've tried to find one based on the specs, but I'm not too confident in my 'component cloning' abilities, I tend to pick the wrong ones. Can someone recommend a comparator that is similar to the LM111?

And regarding the LM567 -- it seems to me, based on the datasheet, that the output when the correct tone is detected should be ground. Or, more specifically, "a saturated transistor switch to ground when an input signal is present within the passband." However, I'm getting a wave on the output. When I get to the correct tone, the duty cycle of the wave goes almost to %0, so if it were averaged out it would essentially be a zero. However when I'm not in the passband, it just gives me a random wave.

Now, my LM567 has a date code of 1993 -- so there's a chance the chip is just fried. If anyone has any experience with this chip, I'd really like to know what the output should be. From the circuits I've found online, it should be essentially a 'digital' 0 or 1 output. One circuit shows it lighting an LED, and I know it can source/sink something like 100ma on the output.

I've got about 3 or 4 LM565's, and if I have a suitable comparator, I'll just use that method to try and get it working. Any and all help is much appreciated!

[David Hess]

The LM111 is hardly obsolete if you consider the commercial temperature range LM311.  In the LM565 datasheet it is just used as a generic fast comparator so any modern comparator appropriate for your output data rate will work.

[MrAureliusR]

Okay, I just thought the LM111 was obseleted, as the particular data sheet I have is marked as obsolete.

The data rate for most RTTY is 45.45 baud, so I get the feeling something as basic as an LM339 or similar would be fine.

Anyone have any info on the LM567/LM565? There doesn't seem to be many projects online where these chips were used. At least, no info on what the output should look like. The data sheet shows a 20k pull up to Vcc, I've got 4.7k I think. Somehow I don't think the pull up being too strong is the problem, but maybe I'll try putting a couple 10k in series and see if there's any difference.

Thanks for the info David!

[David Hess]

Okay, I just thought the LM111 was obseleted, as the particular data sheet I have is marked as obsolete.

The trick here is that the LM111 is the military temperature range version which may very well be obsolete but the LM311 is the commercial temperature range version and will likely live on as long as the LM741.

The data rate for most RTTY is 45.45 baud, so I get the feeling something as basic as an LM339 or similar would be fine.

I think so as well although one reason the LM311 would be used is that its versatile output stage allows it to interface with logic supply voltages while accepting an analog common mode voltage range at its input.  Essentially it can operate with separate analog and digital supply voltages and do the output level shift to drive the logic for free.

[MrAureliusR]

Well, some success at last!

I built up the example circuit in the LM565 datasheet for FSK Demodulation. I used an LM219J comparator, and it seems to be working well. It has similar specs to the LM111/311 as far as I could tell.

I tested the circuit by inputting a simple FM tone, two frequencies back and forth at a constant rate, and the output is a square wave of the same frequency as the modulation on the input, so it seems to be working! Very happy.

However, I'm not sure how well it will work with RTTY. More testing needed... the lower signal fidelity of radio signals might pose a problem. Also, in order to 'tune' the center frequency the potentiometer must be set so that there's an output. I suppose I could use a digital pot and a microcontroller to automate that... just have it look for an output, and keep adjusting the pot until it gets one.

From what I've read, both circuits have their pros and cons. I'm still eager to try out the LM567 as well, because it is actually a dedicated 'tone detector' and I have a feeling that two of them running side by side, each tuned to one of the frequencies in the FSK, would be the ideal demodulator. I know that there are actual FSK demod chips out there -- I believe Exar made some. I know the venerable XR2206 "function generator" chip was part of a line of chips for FSK in old 300 baud modems. I do have an XR2209, which is the VCO, and another Exar chip I can't identify. I remember free_electron mentioning these chips both on the forum and in his Amp Hour feature interview...

Thanks again David for your suggestions! I'm still not fully clear on why regular op-amps don't make good comparators. I know that they work as comparators, but I've always been told they're lousy at it. Does it have to do with the input offset? Or is it another spec that affects it?

[David Hess]

Thanks again David for your suggestions! I'm still not fully clear on why regular op-amps don't make good comparators. I know that they work as comparators, but I've always been told they're lousy at it. Does it have to do with the input offset? Or is it another spec that affects it?

Just off of the top of my head, operational amplifiers make poor comparators because:

1. Their frequency compensation makes them slower.
2. They are not designed to operate in saturation leading to slow recovery times and possibly other problems.
3. Their output stages are not generally logic friendly.
4. Many operational amplifiers, especially precision ones, have low differential input voltage ranges.

Low offset voltage is actually one of the reasons to use an operational amplifier as a comparator.  They have much higher gain allowing them to act on low level signals that a comparator would have problems with.

[sarahMCML]

Anyone have any info on the LM567/LM565? There doesn't seem to be many projects online where these chips were used. At least, no info on what the output should look like. The data sheet shows a 20k pull up to Vcc, I've got 4.7k I think. Somehow I don't think the pull up being too strong is the problem, but maybe I'll try putting a couple 10k in series and see if there's any difference.

Hi,

I've just found the following website which has a backup of many of the original Signetics data books. Your LM567 was originally the NE/SE567, and you can find the 1972 Phase Lock Loop Application Manual at: http://bitsavers.informatik.uni-stuttgart.de/pdf/signetics/_dataBooks/

Hope this is of some use.

[akis]

Hi, I use the LM567 to make sure a tone is at the right frequency, there is some extra circuitry because I think the LM567 requires a low supply voltage, the below schematic lights up an LED when the frequency is right

[Zero999]

Both ICs are a bit long in the tooth but the LM565 is obsolete and no longer available.

Use the LM567 or consider an alternative such as the 74HC4046 or 74HC7046.