sinewave to squarewave converter using LM311

del · Jul 8, 2010

Hi everyone,

Just joined.

Any suggestions on how to wire up an LM311 as a sinewave to squarewave converter. The input signal is a burst signal comprising 5 nos. ~2Vpeak-peak, 200KHz sinewaves repeated every 5msecs. Will be using a single supply of 5Vdc.

Roff · Jul 8, 2010

What does "5 nos." mean? 5 cycles?
What is the DC level of the signal? What is the source impedance?

MRCecil · Jul 8, 2010

If it were me, I would use an LM393 comparator. It would do what you want easily. Here is a link to the National Semi. datasheet:

https://www.electro-tech-online.com/custompdfs/2010/07/LM193.pdf

del · Jul 9, 2010

Sinewave to squarewave convereter using lm311

Thanks everyone for the responses.

Rolf, I do apologize for the incorrect technical term. Yes, its 5 cycles. The input signal doesn't contain any DC level. The signal is the output from the collector of a 2N3904 small-signal amplifier circuit - not sure of the impedance.

MRCecil, could you provide links for the circuit? Would I require feedback (hysteresis)? I tried an LM311 (without hysteresis and single 5V supply) but got a lot of noise at the output and no squarewave. I have attached the implemented circuit. Simulated okay in PSpice Orcad and worked well with input from a signal generator.
Appreciate your suggestions. The input signal is a burst of 5 cycles of ~2Vp-p, 200KHz sinewaves repeated every 5msec.

del

ericgibbs · Jul 9, 2010

del said:
Thanks everyone for the responses.

Rolf, I do apologize for the incorrect technical term. Yes, its 5 cycles. The input signal doesn't contain any DC level. The signal is the output from the collector of a 2N3904 small-signal amplifier circuit - not sure of the impedance.

MRCecil, could you provide links for the circuit? Would I require feedback (hysteresis)? I tried an LM311 (without hysteresis and single 5V supply) but got a lot of noise at the output and no squarewave. I have attached the implemented circuit. Simulated okay in PSpice Orcad and worked well with input from a signal generator.
Appreciate your suggestions. The input signal is a burst of 5 cycles of ~2Vp-p, 200KHz sinewaves repeated every 5msec.

del

hi del.
Post your spice asc file.
To stop the oscillation you need a little positive feedback fro output to non inv input, try a 100K thru 1meg

del · Jul 9, 2010

Hi everyone,

Many thanks ericgibbs for the advice.
Will include the feedbackl resistor.
How do I get the .asc file from PSpice that you requested?

del

Samad Khan · Jul 9, 2010

del
u just have to make ur circuit in PSpice and save it with any name and .asc extension and attach it here....

crutschow · Jul 9, 2010

del said:
The input signal doesn't contain any DC level. The signal is the output from the collector of a 2N3904 small-signal amplifier circuit - not sure of the impedance.

If the signal is not coupled through a blocking capacitor then it likely has a DC level, if it's coming from the collector of a transistor. If it has no DC level than the waveform will have equal excursions above and below 0V.

Roff · Jul 9, 2010

Samad Khan said:
del
u just have to make ur circuit in PSpice and save it with any name and .asc extension and attach it here....

I don't think a Pspice file will run on LTspice.

MikeMl · Jul 9, 2010

Roff said:
I don't think a Pspice file will run on LTspice.

Most will but not as a schematic. If you have a running PSpice netlist text file, you CAN run that in LTSpice about 95% of the time.

Roff · Jul 9, 2010

MikeMl said:
Most will but not as a schematic. If you have a running PSpice netlist text file, you CAN run that in LTSpice about 95% of the time.

I was specifically referring Samad Khan's post, which suggested that simply changing the file extension on a Pspice file would allow it to run on LTspice.

Roff · Jul 9, 2010

Here's an LTspice sim of my understanding of the OP's circuit.

MRCecil · Jul 9, 2010

del said:
MRCecil, could you provide links for the circuit? Would I require feedback (hysteresis)? I tried an LM311 (without hysteresis and single 5V supply) but got a lot of noise at the output and no squarewave. I have attached the implemented circuit. Simulated okay in PSpice Orcad and worked well with input from a signal generator.
Appreciate your suggestions. The input signal is a burst of 5 cycles of ~2Vp-p, 200KHz sinewaves repeated every 5msec.

del

Hi Del,

There are plenty of different applications shown in the National datasheet I linked.

Roff has posted a sim for the LM311 that meets your specs. I will attach another simulation using the the same circuit (a tip of the hat to Roff for supplying the .asc file), but using National's spice model for the LM393/LM2903. The only difference I can see may be an 80ns rise and fall time without any overshoot with the LM393.

Good Luck,
Merv

Roff · Jul 9, 2010

MRCecil said:
Hi Del,

There are plenty of different applications shown in the National datasheet I linked.

Roff has posted a sim for the LM311 that meets your specs. I will attach another simulation using the the same circuit (a tip of the hat to Roff for supplying the .asc file), but using National's spice model for the LM393/LM2903. The only difference I can see may be an 80ns rise and fall time without any overshoot with the LM393.

Good Luck,
Merv

I am also partial to LM393, unless you need to sink more than about 4mA. I used LM311 because I thought our OP might have them in stock.

MRCecil · Jul 9, 2010

Roff said:
I am also partial to LM393, unless you need to sink more than about 4mA. I used LM311 because I thought our OP might have them in stock.

It will sink only 4ma? I thought it was capable of 12 or 15ma...I'll have to look that up so I don't screw up in the future.

Yes, it was good you did use the LM311 to display its capabilities, and a method of hysteresis he questioned. I found the 393 spice model several weeks ago and wanted to see how it performed in LTS.

Cheers,
Merv

Roff · Jul 9, 2010

MRCecil said:
It will sink only 4ma? I thought it was capable of 12 or 15ma...I'll have to look that up so I don't screw up in the future.

Yes, it was good you did use the LM311 to display its capabilities, and a method of hysteresis he questioned. I found the 393 spice model several weeks ago and wanted to see how it performed in LTS.

Cheers,
Merv

LM393 worst case sink current is 4mA@700mV. Typically, it drops out of saturation at about 10-20mA.

MRCecil · Jul 9, 2010

Roff said:
LM393 worst case sink current is 4mA@700mV. Typically, it drops out of saturation at about 10-20mA.

Thank You! I had missed that in my latest design for a low freq input (0-1Mhz) for a freq counter preselector. I'll double check the works to ensure it's within specs.

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