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mpy634 ( URGENT )

WILLIE L. MCCAIN
Prodigy 170 points

Other Parts Discussed in Thread: MPY634

now this device will be used as a feedback controller in a digital sinewave generator

with other functions but first i wont to make sure i have the ideam correct of how the part will work

again x1 will hAVE A REF SIGNAL OF LETS SAY 2.5VPK-PK

AT THIS POINT THE OUTPUT FROM THE MPY634 SHOULD SHOW THE OUTPUT OF THE VOLTAGE ON X1AND X2 IS TO GROUND

NOW LETS SAY THE FEEDBACK SIGNAL IS ADJ TO THE SAME AMPLTD. 2.5VPK=PK THE OUTPUT IS STILL THE SAME

NOW LETS SAY WE INCREASE THE FEEDBACK SIGNAl OVER THE 2.5V AND IT SHOULD START TO DECREASE THE OUTPUT VOLTAGE

AND AS WE DECREASE AND MAKE THE SIGNAL ON Y2 THE SAME AGAIN THE OUTPUT SHOULD COME BACK UP ,NOE Y1 IS GOING TO GROUND

NOW AT THIS POINT EVERYTHING SHOULD BE GOOD

NOE LET SAY THAT WE TAKE Z1 TO GROUND AND PUT A DC VOLTAGE OF LETS SAY  1.00VDC THIS SHOULD CAUSE THE OUTPUT TO DROP RAPIDLY

AND AS WE REDUCE THE VOLTAGE ON Z2 THE OUTPUT TO RETURN TO NORMAL

LET ME NO IF THE IDEA IS CORRECT ARE DO I HAVE THE WRONG PINS SELECTED THE WRONG WAY TO GET THE RESULTS

GET BACK ASAP IAM WORKING ON A PROJECT AND I NEED TO NO

THANKS

  • 0
    TI__Genius 12375 points

    Willie,

    I'm not positive I have completely grasped what you're trying to do but I believe your question is how can you change the output signal amplitude using a DC voltage? If you examine the transfer functions given in the datasheet you should see that if you apply a DC voltage to the Z pins, this will not change the amplitude of the output signal but rather will add a DC offset to the signal. It is also important to note that the transfer function of the part includes the open loop gain of the output opamp ("A" in the transfer function equation) and the Z1 pin is often connected to Vout to provide feedback for the part.

    One possible way to change the amplitude using a DC voltage would be to change the scale factor. It might be possible to use a JFET as a variable resistor at the SF pin, using a DC voltage at the gate, to change the scale factor of the transfer function and hence change the amplitude of the output signal. This would be a new application and hasn't been investigated or characterized though.

    If this is not the question you were asking, then I may need clarification on exactly how you have the MPY634 configured. A clear, concise description and any associated schematics will help me provide the best applications support possible.

  • 0 in reply to John Caldwell
    Prodigy 170 points

    OKAY

    X1=+ INPUT THIS IS WHERE THE REF SINEWAVE WILL BE AT 3VPK-PK AND X2 IS GROUNDED

    Y2=- INPUT THIS IS WHERE THE FEEDBACK SIGNAL WILL GO SINEWAVE ALSO

    Z1 IS CONNECTED TO THE OUTPUT

    Z2 IS THE SUM INPUT

    NOW LETS SAY WE LOOK AT THE FEEDBACK INPUT Y2 AND LETS SAY THE SIGNAL COMMING IN IS THE SAME AS THE REF INPUT X1

    THE OUTPUT SHOULD HAVE NO CHANGE TO AMPLTD, WE ADJ THE OUTPUT TO ZERO OFFSET BY PUTTING A VOLTAGE INTO Z2

    OKAY NOW AS THE FEEDBACK SIGNAL GO ABOVE THE REF SIGNAL ON X1 THE OUTPUT SHOULD START TO DECREASE AND AS IT DECREASES THE OUTPUT SHOULD COME BACK TO THE SAME LEVAL

    AND IF WE NEED TO ADD GAIN TO THE OUTPUT SIGNAL WE WOULD APPLY A DC VOLTAGE LETS SAY 0 TO 2 VDC

    TO THE SF INPUT PIN#4

    THIS IS HOW I THINK THE PART SHOULD WORK / FUNCTION SEE IF THIS IS CLEAR ENOUGHT NOW TO SEE IF IAM CORRECT

    THANKS, AGAIN

    WILLIE

  • 0 in reply to WILLIE L. MCCAIN
    TI__Genius 12375 points

    Willie,

    Applying a DC voltage directly to the SF pin would not properly adjust the output amplitude of the signal and may damage the part. In order to adjust the scale factor, you will need to connect a resistive element from the SF pin to the -Vs supply, this may be a fixed resistor, potentiometer, JFET, etc. The equation at the top of page 6 in the datasheet can be used to determine the value of this element in order to produce the desired change in the output amplitude. However, this equation only specifies accuracy within 25% and you will need to test this design to arrive at working results that meet your specifications.