HSP50307

HSP50307 December 1996 Burst QPSK Modulator Description The HSP50307 is a mixed signal burst QPSK Modulator for upstream CATV Applications. The HSP50307 demultiplexes and modulates a serial data stream onto an RF Carrier centered between 8 and 15MHz. The signal spectrum is shaped with α = 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 75Ω . 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. The HSP50307 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. PKG. NO. M28.3 Features 256 KBPS Data Rate and 128 KBPS Baud Rate Burst QPSK Modulation Programmable Carrier Frequency from 8MHz to 15MHz With a Frequency Step Size of 32kHz α = 0.5 Root Raised Cosine (RRC) Filtering For Spectrum Shapin...