ASCEL Electronic AE20125, Руководство по сборке и эксплуатации

Страница: 9 / 52

Circuit Description
The AE20125 Function Generator is based upon a Direct Digi-
tal Synthesizer (DDS). DDS uses a processor to calculate the
output waveform and a Digital-to-Analog Converter (DAC) to
create the actual voltage needed to produce a waveform. DDS
has the advantage of high accuracy and resolution.
Note: for a comprehensive overview of DDS, an excellent
document is available from Analog Devices
1
.
The heart of the AE20125 is the AD9833 from Analog Devices
(IC2). It is capable of producing sine, square, and triangle wa-
veforms. The 25 MHz crystal oscillator Q1 provides the master
clock for the DDS. The output signal of the DDS is discretely
constructed from a finite number of steps. This signal always
contains unwanted high frequency components. A reconstructi-
on filter is needed to remove these components from the signal.
The filter is composed of L1, C4, L2, C5, L3, C11 and R8. As
the square wave signal does not require filtering, the filter is di-
sabled with the relay K1 when switched to square wave. The
square wave produced by the AD9833 has a different amplitude
than the other waveforms, so the divider R14/P4 adjusts it to
match the amplitude of the sine and triangle wave.
IC1 is the microcontroller that controls the device. The keys
and the LCD are connected to it. The FTDI FT230XS UART-
to-USB-Bridge (IC6) provides USB connectivity to the
microcontroller.
1 A Technical Tutorial on Digital Signal Synthesis, 1999,
http://www.analog.com/static/imported-
files/tutorials/450968421DDS_Tutorial_rev12-2-99.pdf
2