PC's serial port controls programmable sine-wave generator

摘要

This Design Idea describes a circuit that uses a PC's serial port to control a sine-wave generator that covers a frequency range of 2 Hz to 20 kHz in 1-Hz steps (Figure 1). The circuit's output voltage of approximately 2.2V p-p remains constant over the entire frequency range. The circuit's signal source, a Linear Technology (www.linear.com) LTC6904, IC{sub}1, consists of a digitally programmable square-wave oscillator that, without using a clock crystal, covers a frequency of approximately 1 kHz to 68 MHz at 0.1 resolution and a few percentage points of accuracy. The LTC6904 features an PC serial-communications interface that controls the output frequency according to: OSC{sub}(CLK)=2a × 2078 Hz/2-(b/1024). The variables "a" and "b" represent 4- and 10-bit digital codes, respectively, and the equation's frequency unit, OSC{sub}(CLK), is in hertz.