Design Realization lecture 16课件.ppt

Design Realization lecture 16 John Canny 10/16/03 精品文档 Last Time Basic electronics: Resistors, capacitors, inductors, amplifiers 精品文档 This time Analog-Digital boundary Printed-circuit board design 精品文档 Digital-analog boundary Because of the very high performance and programmability of digital circuitry, the goal today is to do as much as possible in the digital realm, and only move to analog at the edges of the system. The design problem then is to choose the right AD and DA converters, and add any necessary analog circuitry around them. 精品文档 Frequency and wavelength Recall that the frequency of an sinusoidal AC signal is the number of complete cycles in a second. As an AC signal propagates as sound or radio, it traces out a sinusoidal signal in space as well. The length of a complete cycle is the wavelength where v is the speed of propagation. 精品文档 Frequency and wavelength For sound, v is about 343 m/s, so ? in meters = 343/f with f in Hz. For light or radio, v is about 3 x 108 m/s. A convenient form is  ? in meters = 300/f with f in MHz. 精品文档 Frequency spectrum 20Hz-20,000 Hz, Audio frequency (for humans) 20 kHz – few MHz (sound) ultrasonics 30 kHz – 300 kHz (radio) long wave, over the horizon radio and radar. 300 kHz – 3MHz, medium-frequency radio, AM 3 MHz – 30 MHz, high-frequency radio (CB and short wave), long-range propagation common. 30-300 MHz, very-high frequency (VHF) radio, FM stations, some TV, Line-of-sight only. Slow computer clock speeds. 精品文档 Frequency spectrum (contd.) 300 MHz - 3 GHz, ultra-high frequency (UHF), some TV, cell phones, microwave ovens, Wi-Fi, GPS, fast computer clock speeds. 3GHz – 30GHz, microwave communications including satellite TV 30GHz – 300 GHz, exotic microwave systems 300GHz – 3THz, microwave-IR DMZ 3THz - 300THz (100 ?m - 1?m) infrared, C02 and YAG lasers. 700 nm – 400 nm visible light. 精品文档 Digital-analog conversion Simplest method: PWM or Pulse-Width Modulation. Adjust the off-time of a p