MPP Coil And Preamp Speed

[green]

I have a MPP with a LM4562 for the amplifier. Was testing frequency response with a 7.8V square wave. 10R to common in series with 40k to square wave out. 10R connected to Rx input. Step response less than I expected. paralleled the input and fdbk resistor and got step response closer to what I expected. Wondering why step response is higher with normal circuit resistors? I posted the question in another thread and didn't get an answer, hoping someone reads this in MPP projects and answers the question.

[green]

Tried with spice using LT6234(60MHz) instead of LM4562(55MHz). Adding 10pf across the 33k fdbk resistor gives a step response close to what I get with the MPP with a LM4562. Never tried to do a circuit board layout so don't know if 10p unwanted capacitance across fdbk could be possible or should I be looking for another reason for the longer step response. Just trying to learn something.

[green]

Tried with spice using LT6234(60MHz) instead of LM4562(55MHz). Adding 10pf across the 33k fdbk resistor gives a step response close to what I get with the MPP with a LM4562. Never tried to do a circuit board layout so don't know if 10p unwanted capacitance across fdbk could be possible or should I be looking for another reason for the longer step response. Just trying to learn something.

Surprised I'm not getting any replies. Maybe a stupid question, maybe something I have done wrong with the MPP I'm using. Would be interested if anyone with a MPP could scope amplifier out TP3 with a square wave input at Rx. 10R across Rx with a resistor in series to reduce signal in to less than 2mV. NE5532 or LM4562, both if you have them. Would also be interested in what the calculated step response is using a NE55322 or LM4562. Thanks

[godigit1]

Hi Green,
Could you please draw a little schematic of your test set up and frequency you are testing at? I will try to match results.
The possibility of a fake chip may explain our differance in coil speed and damping we were seeing.
Best Regards
.

[Polymer]

Hi green,

I have a populated MPP E board with socketed ICs, so could swap chips. I have 5532 and 4562 OPAs.

The only square wave generator I have at the moment is the test output from the oscilloscope. Would that be OK?

I agree with godigit1, please do post a schematic of what goes where for the measurements ... preferably one for dummies :-)

Maybe we can help you get this sorted.

[green]

godigit and Polymer, thanks for the reply. Tried something this morning think you can try. 10R and 30k probably not critical, something close.

Been using a square wave oscillator made with a TLC555. Circuit I could test MPP and my differential amplifier. Think should be lower frequency, signal didn't have time to flat top. I'll play with it some more and get back.

[green]

More. Looked at my scope square wave out, can't use because lot slower than the amplifier. Maybe something wrong with it.

Including a schematic for the 555 oscillator. Used a TLC555 instead of NE555 from schematic.

Used updated oscillator as input to MPP. Response similar to using MPP timer out.

[Polymer]

Hi green, checked my square waves from the oscilloscope.

At scope probes x10 I am getting about 320ns rise time & 140ns fall time.
At scope probes x1 I am getting about 800ns rise time & 400ns fall time.

Maybe the loading of the signal is changing things ... for lack of better explanation.

Hows the schematic for testing going?

[godigit1]

I was wondering about frequency. Was thinking slew rate limited just did not know why.

I checked my signal generator and it only goes down to 4 mV that's pushing it allot of noise at that level.
Cleans up at 60 mV I figured a voltage devider 50k and 25 k will do it.

Confused about the hook up still 10r and 30 k to pin 7??? on the Mpp schem 7 is not connected anything on the sample generator. Thinking you meant pin 6 sneaky way around the signal gen maybe use the c sample out?

Thinking maybe a print of the Mpp Schematic with connections might be a way to go Ill try to put together what Im seeing so far.
Thanks.

[green]

Hi green, checked my square waves from the oscilloscope.

At scope probes x10 I am getting about 320ns rise time & 140ns fall time.
At scope probes x1 I am getting about 800ns rise time & 400ns fall time.

Maybe the loading of the signal is changing things ... for lack of better explanation.

Hows the schematic for testing going?

Schematic. Could try your scope square wave, pin7 of U6 or U7 of MPP or other step signal generator(step time<.5us, longer than 10us)?

Shorter the step time the better.

[green]

I was wondering about frequency. Was thinking slew rate limited just did not know why.

I checked my signal generator and it only goes down to 4 mV that's pushing it allot of noise at that level.
Cleans up at 60 mV I figured a voltage devider 50k and 25 k will do it.

Confused about the hook up still 10r and 30 k to pin 7??? on the Mpp schem 7 is not connected anything on the sample generator. Thinking you meant pin 6 sneaky way around the signal gen maybe use the c sample out?

Thinking maybe a print of the Mpp Schematic with connections might be a way to go Ill try to put together what Im seeing so far.
Thanks.

30k goes to pin7, poked resistor lead to pin7 dip package.

[Polymer]

Cannot find U6/U7 where I assume they should be. I dont want to second guess here.
For the sake of clarity, here the schematic I am using (MPP version E):



My oscilloscope output is 5v pp. Oddly enough measuring 0v to +5v in DC mode and -2.5 to +2.5v in AC mode

So at 5v a 25k resistor would do in series to the 10 Ohm one. Resulting voltage across Rx to GND would be 2mV (for test)?

[godigit1]

Hi Polymer,

This is the voltage divider calculator I used.
http://www.ohmslawcalculator.com/vol...der-calculator.


That would be U7 U10 on the rev E.
Think I need to scope Pin 7 see what I'm missing. Ill have some time today I hope.

[green]

I didn't have a signal generator so I made one with a 555. Tried using sample generator for the step input so all our comparisons would be the same, and wouldn't need an external signal generator. Shouldn't matter if step response is fast enough and step time long enough.

Been calling it square wave but only needs a fast step voltage with long enough step times.

[green]

Surprised I'm not getting any replies. Maybe a stupid question, maybe something I have done wrong with the MPP I'm using. Would be interested if anyone with a MPP could scope amplifier out TP3 with a square wave input at Rx. 10R across Rx with a resistor in series to reduce signal in to less than 2mV. NE5532 or LM4562, both if you have them. Would also be interested in what the calculated step response is using a NE55322 or LM4562. Thanks

Trying some things in spice. Step time to flat approximately equal to(closed loop gain/amplifier BW). Needed to parallel fdbk resistor with a capacitor to prevent overshoot with some of the amplifiers I tried. Calculated step time to flat LM4562(33/55e6)=.6us NE5532(33/10e6)=3.3us

Thinking measured step time to flat should be less than desired target TC?