HSP50307

The HSP50307 is a mixed signal burst QPSK Modulator for upstream CATV Applications. It demultiplexes and modulates a serial data stream onto an RF Carrier centered between 8 and 15MHz. The signal spectrum is shaped with a = 0.5 root raised cosine (RRC) digital filters. On-chip filtering limits spurs and harmonics to levels below -35dBc during transmissions. The output power level is adjustable over a 40dB range in 1dB steps. The maximum differential output level is +62dBmV into 75W. A transmitter inhibit function disables the RF output outside the burst interval. The differential output amplifier int7-erfaces to the cable via a transformer. The Block Diagram of the HSP50307 QPSK Modulator is shown below. It consists of a digital control interface, an I/Q generator, a synthesizer, and a quadrature modulator.

The data clock is derived from the master clock. The HSP50307 demultiplexes the input data bits into in-phase (I) and quadrature (Q) data streams. The first bit and subsequent alternating bits of the burst are in-phase data. The two data streams are filtered, converted from digital to analog, and low pass filtered to produce the baseband I and Q analog signals.

The baseband signals are up-converted to RF in the Quadrature Modulation Section HSP50215EVAL. The synthesizer provides the local oscillator (LO) for the quadrature modulator. The frequency is programmable via the control interface with a resolution of 32kHz. The output of the quadrature modulator is low pass filtered to remove harmonic distortion.