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參數資料
| 型號： | AD8138ARMZ-REEL |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | 通用總線功能 |
| 英文描述： | Low Distortion Differential ADC Driver |
| 中文描述： | LINE DRIVER, PDSO8 |
| 封裝： | LEAD FREE, MO-187AA, MSOP-8 |
| 文件頁數： | 20/24頁 |
| 文件大小： | 318K |
| 代理商： | AD8138ARMZ-REEL |
AD8138
BALANCED TRANSFORMER DRIVER
Transformers are among the oldest devices used to perform a
single-ended-to-differential conversion (and vice versa). Trans-
formers can also perform the additional functions of galvanic
isolation, step-up or step-down of voltages, and impedance
transformation. For these reasons, transformers always find
uses in certain applications.
Rev. F | Page 20 of 24
However, when driving the transformer in a single-ended
manner, there is an imbalance at the output due to the parasitics
inherent in the transformer. The primary (or driven) side of the
transformer has one side at dc potential (usually ground), while
the other side is driven. This can cause problems in systems that
require good balance of the transformer’s differential output
signals.
If the interwinding capacitance (C
STRAY
) is assumed to be
uniformly distributed, a signal from the driving source couples
to the secondary output terminal that is closest to the primary’s
driven side. On the other hand, no signal is coupled to the
opposite terminal of the secondary because its nearest primary
terminal is not driven (see Figure 43). The exact amount of this
imbalance depends on the particular parasitics of the trans-
former, but is mostly a problem at higher frequencies.
The balance of a differential circuit can be measured by
connecting an equal-valued resistive voltage divider across the
differential outputs and then measuring the center point of the
circuit with respect to ground. Since the two differential outputs
are supposed to be of equal amplitude, but 180° opposite phase,
there should be no signal present for perfectly balanced outputs.
The circuit in Figure 43 shows a Mini-Circuits T1-6T
transformer connected with its primary driven single-endedly
and the secondary connected with a precision voltage divider
across its terminals. The voltage divider is made up of two
500 Ω, 0.005% precision resistors. The voltage V
UNBAL
, which is
also equal to the ac common-mode voltage, is a measure of how
closely the outputs are balanced.
Figure 45 compares the transformer being driven single-
endedly by a signal generator and being driven differentially
using an AD8138. The top signal trace of Figure 45 shows the
balance of the single-ended configuration, while the bottom
shows the differentially driven balance response. The 100 MHz
balance is 35 dB better when using the AD8138.
The well-balanced outputs of the AD8138 provide a drive signal
to each of the transformer’s primary inputs that are of equal
amplitude and 180° out of phase. Therefore, depending on how
the polarity of the secondary is connected, the signals that
conduct across the interwinding capacitance either both assist
the transformer’s secondary signal equally, or both buck the
secondary signals. In either case, the parasitic effect is
symmetrical and provides a well-balanced transformer output
(see Figure 45).
PRIMARY
C
STRAY
C
STRAY
52.3
SECONDARY V
DIFF
500
0.005%
500
0.005%
V
UNBAL
SIGNAL IS COUPLED
ON THIS SIDE VIA C
STRAY
NO SIGNAL IS COUPLED
ON THIS SIDE
0
Figure 43. Transformer Single-Ended-to-Differential Converter Is Inherently
Imbalanced
V
DIFF
V
UNBAL
AD8138
+IN
–IN
OUT+
OUT–
499
499
499
499
49.9
49.9
500
0.005%
500
0.005%
C
STRAY
C
STRAY
0
Figure 44. AD8138 Forms a Balanced Transformer Driver
FREQUENCY (MHz)
0
O
–20
–40
–60
–80
–100
0.3
1
10
100
500
V
UNBAL
, DIFFERENTIAL DRIVE
V
, FOR TRANSFORMER
WITH SINGLE-ENDED DRIVE
0
Figure 45. Output Balance Error for Circuits of Figure 43 and Figure 44
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| AD8138ARMZ-REEL7 | Low Distortion Differential ADC Driver |
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| AD8138ARZ-R7 | Low Distortion Differential ADC Driver |
| AD8138ARZ-RL | Low Distortion Differential ADC Driver |
| AD8138 | Low Distortion Differential I/O Amplifier(小失真差分輸入/輸出放大器) |
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| AD8138AR-REEL7 | 功能描述:IC AMP DIFF LDIST LP 95MA 8SOIC RoHS:否 類別:集成電路 (IC) >> 線性 - 放大器 - 專用 系列:- 產品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:60 系列:- 類型:可變增益放大器 應用:CATV 安裝類型:表面貼裝 封裝/外殼:20-WQFN 裸露焊盤 供應商設備封裝:20-TQFN-EP（5x5） 包裝:托盤 |
| AD8138ARZ | 功能描述:IC AMP DIFF LDIST LP 95MA 8SOIC RoHS:是 類別:集成電路 (IC) >> 線性 - 放大器 - 專用 系列:- 產品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:60 系列:- 類型:可變增益放大器 應用:CATV 安裝類型:表面貼裝 封裝/外殼:20-WQFN 裸露焊盤 供應商設備封裝:20-TQFN-EP（5x5） 包裝:托盤 |
| AD8138ARZ-R7 | 功能描述:IC AMP DIFF LDIST LP 95MA 8SOIC RoHS:是 類別:集成電路 (IC) >> 線性 - 放大器 - 專用 系列:- 產品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:60 系列:- 類型:可變增益放大器 應用:CATV 安裝類型:表面貼裝 封裝/外殼:20-WQFN 裸露焊盤 供應商設備封裝:20-TQFN-EP（5x5） 包裝:托盤 |
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