参数资料
| 型号： | ISL6421ER-T |
| 厂商： | Intersil |
| 文件页数： | 1/18页 |
| 文件大小： | 0K |
| 描述： | IC REG SGL LNB CONTROL 32-QFN |
| 标准包装： | 6,000 |
| 应用： | 转换器，卫星信号接收机顶盒设计 |
| 输入电压： | 8 V ~ 14 V |
| 输出数： | 1 |
| 输出电压： | 13 V ~ 18 V |
| 工作温度： | -20°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 32-VFQFN 裸露焊盘 |
| 供应商设备封装： | 32-QFN（5x5） |
| 包装： | 带卷 (TR) |
?
ISL6421, ISL6425 Single LNB Controllers with I 2 C
Interface for Advanced Satellite Set-Top Box Designs
PRELIMINARY
Application Note
May 6, 2005
AN1083.1
Introduction
Communication Satellite Frequency Allocation
Communication satellites operate within two frequency
bands for TV/Broadband service broadcast signals, C Band
and Ku Band. The C Band overall frequency spectrum is
4.0GHz -8.0GHz, while the Ku Band overall frequency
spectrum is 11.7GHz -18.0GHz.
Within these bands each satellite will have specific uplink
and downlink frequency allocation. For example the North
American DBS system has categories assigned as follows,
Ku Band high power downlink is 12.2GHz-12.7GHz and
17.3GHz-17.8GHz as the uplink frequency, C Band downlink
frequency is 3.7GHz -4.2GHz and 5.925GHz -6.425GHz as
uplink frequency.
Also, to use the frequencies that are available for satellite
broadcast as efficiently as possible, and to accommodate an
additional number of channels within a given frequency
band, the transmission signal can be formatted to be either
vertical and horizontal, or circular right-hand and circular left-
hand simultaneously per frequency.
What is a Low Noise Block (LNB)?
An LNB is a low noise block module, placed on the focus of
the dish antenna (parabola) that provides the following
functions:
? Down conversion of the incoming signal from GHz range
to the 910MHz-2150MHz (for Europe) range called “first
conversion signal.” This conversion allows the signal to be
carried by an inexpensive coaxial cable towards the
receiver.
? Signal amplification with good noise figure. The LNB
improves the first conversion signal level through the use
of a built-in low noise amplifier.
? Selection of Vertical or Horizontal polarization.
? Selects operating band by switching its internal oscillator
from Low band to High band when the LNB “receives” a
22kHz tone. Specifically, the local oscillator (LO)
frequency changes from 9.75GHz to 10.6GHz.
C Band - LO frequency 9.75GHz
Ku Band - LO frequency 10.6GHz
? Miscellaneous functions based on 22kHz tone PPM
encoding, as discussed later in this paper.
Polarization Selection
Polarization is a way to give a transmission signal specific
direction. It increases the beam concentration. The signal
transmitted by satellite can be polarized in one of four
different ways: Linear (horizontal or vertical) or Circular
(right-hand or left-hand). Consequently, the satellite can
broadcast both H and V or LH and RH polarized signals on
one frequency.
The “universal” LNB switches the polarization by looking at
the voltage that it receives from the receiver.
12V – Horizontal, 18V – Vertical
13V – Circular right-hand, 20V – Circular left-hand
Generally, only two (12V and 18V or 13V and 20V) will be
used with one type of antenna. Also, 1V can be added from
a receiver to any of above voltages to compensate for the
voltage drop in the coaxial cable, i.e., it could be 13V (12V),
14V (13V), 19V (18V) or 21V (20V) instead.
22kHz Tone and DiSEqC (Digital Satellite
Equipment Control) Encoding
In addition to selecting the polarization, the LNB needs to
select the operating band. This is done with the use of a
22kHz tone frequency. A 22kHz pulse-position modulated
signal of about 0.6V amplitude is superimposed on the
LNB’s DC power rail. Its coding scheme allows the remote
electronics to perform more complex functions like varying
the down conversion frequency to select one of multiple
LNB’s for dual-dish systems or physically rotating the
antenna assembly. Traditionally, when other encoding
functions do not require using 22kHz tone, simple presence
or absence of this tone selects the operating band by
changing the local oscillator frequency of the LNB.
The complex encoding of the 22kHz burst is done with a
more sophisticated communication bus protocol named the
DiSEqC standard (Digital Satellite Equipment Control). The
open DiSEqC standard developed by the European
Telecommunication Satellite Organization is a well accepted
worldwide standard for communication between satellite
receivers and satellite peripheral equipment.
The 22kHz oscillator has to be a tone generator with specific
rise and fall time. The wave shape will be a quasi-square
wave (sine with flat-top). The required frequency tolerance is
±2kHz over line and temperature variations. Burst coding of
this signal is accomplished by input from the microcontroller
at the DSQIN pin of the IC or by setting the ENT bit of the
system register through the I 2 C bus as detailed in the
ISL6421, ISL6425 datasheets.
22kHz WAVE SHAPE AND DETAILS (See Figures 1 and 2)
Carrier frequency: 22kHz ±2kHz over line and temperature
Carrier amplitude: 650mVpp ±250mV
Modulation mark period: 500μs ±100μs
Modulation space period: 1ms ±200μs
1
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 1-888-468-3774 | Intersil (and design) is a registered trademark of Intersil Americas Inc.
Copyright Intersil Americas Inc. 2003, 2005. All Rights Reserved
All other trademarks mentioned are the property of their respective owners.
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