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  1. #1
    Newbie level 3
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    Help with my precise FSK modulator

    Want to create a ultrasound fsk modulator ( sine wave ) with fo at 20KHz and f1 at 20.5KHz

    First, we used XR2006, but its frequency accuacy is only 1%, which is not good enough for our project,

    Then, we changed to use a avr mega microntroller, but its pwm output is too slow.

    Now we start to think about using mcu + DAC ( high speed ), letting mcu output more than 30 values during a sine circle and DAC translate it to voltage. Is that a good design> We are not sure.

    We wonder whether there is a more precise XR2206 in market or any other popular solution for problems like this.

    Thanks for any suggestions.

    •   Alt24th June 2011, 23:34

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  2. #2
    Advanced Member level 4
    Points: 10,248, Level: 24

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    Re: Help with my precise FSK modulator

    Hi Marius,

    instead of generate sinusoidal waves with PWM, DAC or an analog waveform generator, you can use your microcontroller (or other digital circuit) for generate a square wave at f0 and f1. Then, filter the square-wave FSK with a low-pass or passband filter. That filter has to pass the band centered at about 20 KHz, and the lower band that has to stop is centered at about 60 KHz (the 3rd harmonic) if the square wave has 50% duty cycle. The filter has not stringent requirements.
    Regards

    Z



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