METHOD OF LPF FILTERING, LPF USING THE METHOD AND PCM/FM MODULATION SYSTEM

摘要

PURPOSE: A method of LPF filtering, LPF using the method and a PCM/FM modulation system are provided to control the characteristics required for filtering by using one filter hardware. CONSTITUTION: A PCM coder(110) outputs a variable PCM bit stream. A low-pass filter(120) performs a pulse modulation for limiting the RF band. A low-pass filter comprises a FIR(Finite Impulse Response) part, a DAC(Digital to Analog Conversion) part(140), and a LPF(Low Pass Filter) part(150). An analog output signal of the low-pass filter is used as an input of a voltage controlled oscillator inside the FM transmitter(160). An oversampling frequency generator(170) supplies over sampling frequency to the FIR part and DAC part. The control voltage input part(180) inputs the control voltage to the LPF. A main controller(190) controls the variable of the LPF and the FIR part.