Reader and transponder 2ASK modem circuit

Published:2011/6/19 23:54:00 Author:John | Keyword: modem, Reader, transponder | From:SeekIC

2ASK’s carrier signal is 2MHz sine wave. It achieves crystal of the square wave through a low pass filter. Digital modulation signal is output from the CPU's serial port and the signals are controlled to on or off through the analog switch MX7501, resulting in 2ASK signals. L1, L2, C1 and C2 constitute the second-order Butterworth low-pass filter, whose output is approximately sine wave’s 2 MHz signals. R1 and R4 lead to the matching of the LC filter impedance. When EN is 0, the OUT is 0; vice versa for the S1 channel signal. The following figure shows the reader’s 2ASK modulation circuit.



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