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參數(shù)資料
| 型號： | LMH6678LQX |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 通用總線功能 |
| 英文描述： | Low Power 2-Channel Central-Office xDSL Driver |
| 中文描述： | DUAL LINE DRIVER, QCC24 |
| 封裝： | 5 X 4 MM, LLP-24 |
| 文件頁數(shù)： | 13/17頁 |
| 文件大?。?/td> | 1792K |
| 代理商： | LMH6678LQX |
Application Notes
(Continued)
R-C TERMINATION CIRCUIT AND TRANSFORMER
TURNS RATIO
The LMH6678 was designed to operate in the circuit of
Figure 5
. In this circuit, resistor R
1
and R
2
provide a line
termination in the upstream band. At higher frequencies in
the downstream band, capacitors C
1
and C
2
bypass R
1
and
R
2
for higher efficiency.
To calculate the transformer turns ratio required, we assume
a peak-to-rms ratio of 5.8 must be supported and the V
supply tolerance is 5%. At a 30
load, the driver outputs can
swing to 350 mV of each rail with low distortion. This gives a
peak swing of 12(.95) 0.7 = 10.7V. A typical selection for
C
, C
, R
and R
results in approximately 0.1 dB loss and
the transformer loss is typically 0.25 dB, so total voltage loss
is about 0.35 dB.
For 19.8 dBm output, line rms voltage is 3.09 and peak
voltage is 17.9. The optimum turns ratio is calculated at
1.035 x 17.9/10.7 = 1.73. This gives a reflected line imped-
ance of 100
/(1.73)
2
= 33.4 at the primary side. R
and R
2
are usually chosen to be 33.4/2 = 16.7 to terminate the line
at lower frequencies.
INPUT POWER LEVEL AND GAIN
With losses included, output power from the LMH6678
should be 19.8 dBm + 0.35 dB = 20.15 dBm or 103.5 mW. At
33.4
, the rms differential output voltage is
√
(PxR) = 1.86
Vrms. The driver amplifiers have a voltage gain of 5.4V/V, so
the input level should be 1.86/5.4 = 344 mV
RMS
to deliver
19.8 dBm to the line.
The driver input equivalent circuit is shown in
Figure 1
. The
inputs should be capacitively coupled to maintain the input
and output common-mode voltage at V
CC
/2.
20084044
FIGURE 4. MTPR Measurement Test Circuit
20084045
FIGURE 5. Typical R-C Termination
L
www.national.com
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| LMH6678 | Low Power 2-Channel Central-Office xDSL Driver |
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| LMH6704MAX | 650 MHz Progammable Gain Buffer with Disable |
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LMH6682 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:190MHz Single Supply, Dual and Triple Operational Amplifiers |
| LMH6682MA | 制造商:Texas Instruments 功能描述:OP Amp Dual Volt Fdbk ±6V/12V 8-Pin SOIC N Rail 制造商:Texas Instruments 功能描述:AMP, VIDEO DUAL, SMD, SOIC8, 6682 |
| LMH6682MA/NOPB | 功能描述:運算放大器 - 運放 RoHS:否 制造商:STMicroelectronics 通道數(shù)量:4 共模抑制比（最小值）:63 dB 輸入補償電壓:1 mV 輸入偏流（最大值）:10 pA 工作電源電壓:2.7 V to 5.5 V 安裝風格:SMD/SMT 封裝 / 箱體:QFN-16 轉(zhuǎn)換速度:0.89 V/us 關(guān)閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel |
| LMH6682MAX | 功能描述:運算放大器 - 運放 RoHS:否 制造商:STMicroelectronics 通道數(shù)量:4 共模抑制比（最小值）:63 dB 輸入補償電壓:1 mV 輸入偏流（最大值）:10 pA 工作電源電壓:2.7 V to 5.5 V 安裝風格:SMD/SMT 封裝 / 箱體:QFN-16 轉(zhuǎn)換速度:0.89 V/us 關(guān)閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel |
| LMH6682MAX/NOPB | 功能描述:運算放大器 - 運放 RoHS:否 制造商:STMicroelectronics 通道數(shù)量:4 共模抑制比（最小值）:63 dB 輸入補償電壓:1 mV 輸入偏流（最大值）:10 pA 工作電源電壓:2.7 V to 5.5 V 安裝風格:SMD/SMT 封裝 / 箱體:QFN-16 轉(zhuǎn)換速度:0.89 V/us 關(guān)閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel |
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