HSP50307 Просмотр технического описания (PDF) - Intersil

Номер в каталоге

Компоненты Описание

производитель

HSP50307

Burst QPSK Modulator

Intersil 

HSP50307

Pin Description (Continued)

SYMBOL TYPE

DESCRIPTION

AVCC

I Positive supply for the synthesizer (+5V analog). (P)

VCO_SET

I/O VCO free running frequency set resistor (normally 6.25kΩ). (D)

VCO_IN

I Voltage-controlled oscillator control voltage. (D)

PD_OUT

O Phase/frequency detector output. (D)

AGND

I Negative supply for the synthesizer. (P)

RCLK

I Synthesizer reference clock input (2.048MHz). (D)

DVCC

I Positive supply for the digital filters and control (+5V digital). (P)

C_EN

I Control interface enable for 3 wire interface. See Control Interface Section. (D)

CDATA

I Serial data input for 3 wire interface. See Control Interface Section. (D)

CCLK

I

3 wire interface clock. See Control Interface Section. (D)

NOTE: (A) = analog, (D) = digital, (P) = power.

Functional Description

The HSP50307 is designed to transmit 256 KBPS data

using QPSK modulation on a programmable carrier over

75Ω cable lines. The incoming 256 KBPS data is first

demultiplexed into in-phase (I) and quadrature (Q) data

streams. The burst QPSK modulator shapes the two

128 KBPS demultiplexed data streams using interpolate-

by-8 root-raised cosine (RRC) filters with α = 0.5. The

resulting 1.024MHz data streams are sent through D/A

converters and are then sent through low-pass

reconstruction filters for over 40dB image rejection. The

baseband analog output and input pins allow the signals to

be AC coupled. The returning analog signal is upconverted

by an analog quadrature modulator. The control section is

configured by loading 23 bits of information via a three-wire

interface. These bits configure the DSP filter section, the

carrier frequency, the analog synthesizer, and the output

driver sections.

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

-0.1

-0.2

1

8

16

24

32

40

48

56 64

TAP NUMBER

FIGURE 1. NORMALIZED IMPULSE RESPONSE OF THE RRC

INTERPOLATION FILTER WITH α = 0.5

Digital Filters

The burst QPSK modulator uses an interpolate-by-8 digital

RRC filter on both the I and Q data streams. The shaping

factor is set to α = 0.5. The FIR order of the digital RRC filter

is 64. Figure 1 shows the impulse response of the RRC filter.

Figure 2 is a spectrum analyzer plot of the modulator output

for a baud rate of 128 kbaud and a pseudorandom data pat-

tern. The 128kHz 3dB bandwidth and 192kHz stopband

edges are readily apparent.

REF -15.0 dBm

PEAK

LOG

5dB/

WA SB

SC FS

CORR

# AT 60dB

MKR 8.0960MHz

-16.83dBm

CENTER 8.0960MHz

#RES BW 300Hz

VBW 300Hz

SPAN 400.0kHz

SWP 13.3s

FIGURE 2. SPECTRUM OF 8.096MHz RANDOM DATA MODU-

LATED CARRIER

3

Share Link: