Am transmitter - vlsi project

Discussion in 'Wireless & RF Design' started by hanan, Oct 26, 2006.

  1. hanan

    Thread Starter New Member

    Oct 26, 2006
    I need to design an AM transmitter as a vlsi project (it needs to be
    located on smart dust later on).
    Does anyone have any good suggestions were to start from? I am familiar
    with vlsi, but don't really know how to implement such a big idea, into
    a vlsi simulation and circuit design.
    Looking on trasmitter's schemes didn't help, 'cause that's all
    resistors, amplifiers and capacitors. How do I translate it into a vlsi
    designed with cmos?
    generally, it's for smart dust, so the power is very low, around
    several mili volts, frequecny:
    An amplitude modulated signal for typical AM broadcasts consists of a
    sinusoid with a frequency in a range from 0.535 MHz to 1.604 MHz having
    an amplitude
    that is varied (modulated) by an audio signal with frequencies of 20 Hz
    to 5KHz.
    Be very glad to any guidance...
  2. beenthere

    Retired Moderator

    Apr 20, 2004

    Transmitters tend to be full of amps, resistors and capacitors, with the odd inductor thrown in here and there.

    It sounds as if it might be exceptionally challenging to implement even a low-power AM transmitter all in VLSI. You will have to be able to emulate every aspect of analog signal processing.

    How were you planning to do AM modulation on your carrier?
  3. Papabravo


    Feb 24, 2006
    I could be wrong, but VLSI is usually applied to digital signals and circuits with "regular" structures like ROM and RAM. Typically analog and digital circuits have different requirements when it comes to silicon. When the two are placed together on the same substrate it is called mixed signal technology.

    As I see it controlling things like impedance, crosstalk, and interference is way more difficult on a chip then on a chassis, especially when the power levels get high as you would expect them to in a transmitter.

    I don't mean to be a buzzkill, but you might want to adjust your expectations.
  4. Søren

    Senior Member

    Sep 2, 2006

    To do AM modulation with logic, you could cheat and use PWM (or similar) at a much higher frequency, but then it's not really AM, although it would look just like it after the harmonics filtering (L's and C's) that you'd need afterwards/outside the chip any-which-way you make it.

    It's hard to AM modulate states of True/False (unless you're a politician ;))
  5. n9352527

    AAC Fanatic!

    Oct 14, 2005
    Assuming that by smartdust you are referring to the grain-of-sand size, then with such a low frequency, you'd probably end up not with a smart dust but with something the size of a credit card. As a rule of thumb, the lower the frequency is, the bigger the area needed for the frequency dependent components. If you go UHF (868-930MHz) you could end up with something the size of a smartchip. Going to 2.45GHz will result in a smaller chip. The latter is the possible choice for smartdust applications. There are also designs that use optical comm instead.

    Of course, the transmitter design will have to be adapted for on-chip components only. I would say the chance of successfully linked a simulated design to an actually working product is pretty small if you go with higher frequency. You'd need comprehensive simulation packages, something that deal with high freq. RF or microwave and not just plain analogue simulator like SPICE or digital simulator.

    If this is an exercise only, then I think Papabravo is right, you need to adjust your expectations. But if this is work related, then I guess your company is in a big trouble. This field requires skills that are not transferrable through a forum like this.

    Realistically, you'd probably more comfortable with something like, and the size of, motes instead of smartdust.
  6. SM5JAB

    New Member

    Oct 1, 2007
    At such a low frequency PWM is the way to go. Fully VLSI-compatible digital etc and modulation easily accomplished.