Digital FM radio transmitter working theory

Digital FM transmitter with traditional analog FM transmitter working principle is essentially different. Simply put, the analog FM transmitter VCO + PLL simulation technology, and digital FM transmitter with DSP + DDS, software radio digital technology. Digital FM radio transmitter block diagram is as follows:

How it works:
    Figure can be seen in digital FM transmitter audio signal input unit, digital signal processing unit, digital FM modulation and band pass filtering unit, the zoom power stability and low-pass filter unit, man-machine interface control and communications unit and power supply circuit unit six modular units.
    The audio signal input unit is responsible for receiving the analog audio input signals and digital audio (AES / EBU) input signals, analog audio signals into digital audio analog to digital converter (A / D) into the DSP, digital signal directly into the DSP decided to choose what kind of signal as an input audio signal by the DSP.
    Digital signal processing unit is the key modules of the actuator unit, its core is a high performance 550MHz digital signal processor (DSP), DSP software control of the input digital audio signal gain adjustment, digital filtering, digital pre- increased, the digital pilot occur, digital stereo encoded stereo composite signal code stream, this stream by computing the FM modulation to the actuator baseband stream, thus forming a digital FM stream signal, the stream was sent direct digital frequency synthesizer (DDS), the formation of the FM radio frequency signal into the 1000MHz.
    Digital FM modulation and band-pass filter unit, the core components of a direct digital frequency synthesizer (DDS), it receives the DSP output of the digital FM stream signal to form a digital FM radio frequency signal through the internal direct frequency synthesizer, the built-in number analog converter (D / A), the formation of the analog FM modulated wave signal, the pure FM RF signal after band-pass filter.
    Power stability to enlarge feedback and low-pass filter unit along the closed-loop control (AGC) FM radio frequency power amplifier and low pass filter circuit. Ensures that the output power in long-term stable operation of the power set.
    The man-machine interface control and communication unit using a high performance system on chip (SOC) microprocessor to complete the man-machine interface of the actuator, and run data acquisition, alarm protection, external communications and other functions. A variety of command from the keyboard input, transmitter working state by a large-screen LCD and status indicators in real-time display. Data exchange with the remote computer through a standard RS-232 serial communication interface (or interfaces), in order to achieve the functionality of the remote telemetry.
    Power circuit to provide DC power supply unit for the actuator module unit.