參數資料
型號: HDM8513A
廠商: Hynix Semiconductor Inc.
元件分類: 基準電壓源/電流源
英文描述: Linear Voltage Regulator IC; Package/Case:3-TO-92; Supply Voltage:30V; Output Voltage:5V; Current Rating:0.1A; Operating Temp. Max:70 C; Operating Temp. Min:0 C; Output Voltage Max:5V; Voltage Regulator Type:Positive Voltage
中文描述: 的DVB /決策支持系統(tǒng)兼容接收器
文件頁數: 22/67頁
文件大小: 261K
代理商: HDM8513A
22
3.3 Noise Measurement Circuit
When the DBS system is being installed in any place, the most difficult part of the installation is
accurate pointing of the antenna toward the satellite. Inaccurate pointing results in loss of margin
and greater potential for outages in adverse weather conditions. Existing systems use information
from the demodulator forward error correction circuits to provide a measure of antenna pointing.
Unfortunately, this method is useful over a range of only several dB above system threshold.
The HDM8513A employs a unique circuit for accurate measure of signal strength over a 20 dB
range of signal to noise ratio. This method, illustrated in the block diagram, makes use of the fact
that the demodulator provides 8 bits of resolution for each of the quadrature output components.
This high resolution provides a means of measuring the noise component with great accuracy.
The eight bit in-phase demodulator filter output is detected by an absolute value circuit, then
passed through an IIR to provide a measure of average signal amplitude. Each sample is then
subtracted from this average amplitude to provide an instantaneous noise sample. The absolute
value of these noise samples are then averaged by a second IIR to provide a measure of the noise
which is roughly proportional to the noise power and inversely proportional to signal to noise ratio.
Finally, the Figure 17 illustrates the results of simulations under different noise conditions. This
figure illustrates that for signal-to-noise ratio as high as 19 dB, the noise measurement circuit
provides a meaningful measure of signal power with worst case resolution of 1 dB.
Absolute
Value
R
255
256
8
16
8
Absolute
Value
R
255
256
8
16
8
Component
Average
agnitude
Instantaneous
Deviation
Average
Deviation
In hase
-
F
IGURE
16: N
OISE
M
EASUREMENT
C
IRCUIT
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