參數(shù)資料
型號: AD8123ACPZ
廠商: Analog Devices Inc
文件頁數(shù): 7/16頁
文件大小: 0K
描述: IC RCVR TRPL DIFF EQUAL 40LFCSP
標準包裝: 1
類型: 接收器
驅(qū)動器/接收器數(shù): 0/3
電源電壓: 4.5 V ~ 5.5 V
安裝類型: 表面貼裝
封裝/外殼: 40-VFQFN 裸露焊盤,CSP
供應(yīng)商設(shè)備封裝: 40-LFCSP-VQ(6x6)
包裝: 托盤
AD8123
Rev. A | Page 15 of 16
INPUT COMMON-MODE RANGE
When used, common-mode sync signals are generally applied
with a peak deviation of 500 mV and thereby increase the
common-mode level from 2.675 V to 3.175 V. This common-
mode level exceeds the specified input voltage swing limits of
±3.0 V; therefore, the AD8123 cannot be used with a system
that uses common-mode sync encoding with 500 mV sync peak
deviation and 2.5 V common-mode line level. While it is possible
to operate a driver powered from a single 5 V supply at a common-
mode voltage of <2.5 V to obtain a received voltage swing that is
within the specified limits, there is not much margin for other
shifts in the common-mode level due to interference pickup and
differing ground potentials. There are two ways to increase the
common-mode range of the overall system. One is to power the
driver from ±5 V supplies, and the other is to place an AD8143
in front of the AD8123, as shown in Figure 32. These techniques
may be combined or applied separately.
Most applications that use the AD8123 as a receiver use a driver
(such as one from the AD8146/AD8147/AD8148 family, the
AD8133, or the AD8134) powered from ±5 V supplies. This
places the common-mode voltage on the line nominally at 0 V
relative to the ground potential at the driver and provides optimum
immunity from any common-mode anomalies picked up along
the cable (including ground shifts between the driver and receiver
ends). In many of these applications, the AD8123 input voltage
range of typically ±3.0 V is sufficient. If wider input range is
required, the AD8143 triple receiver (input common-mode
range equals ±10.5 V on ±12 V supplies) may be placed in front of
the AD8123. Figure 32 illustrates how this is done for one channel.
068
14-
03
3
100
49.9
1
2
3
RECEIVED
SIGNAL
+5V
ONE AD8123
INPUT
ONE AD8143 CHANNE L
POWER SUPPLIES = ±12V
–5V
HBAT-540C
SMALL SIGNAL FREQUENCY RESPONSE
Though the AD8123 large signal frequency response
(VO = 1 V p-p) is of most concern, occasionally designers are
interested in the small signal frequency response. The AD8123
frequency response for VO = 300 m V p-p is shown in Figure 33
for 200 meter and 300 meter cable lengths.
Figure 32. Optional Use of AD8143 in Front of AD8123 for
Wide Input Common-Mode Range
06
81
4-
0
32
FREQUENCY (MHz)
GA
IN
(
d
B
)
–12
–11
–10
–9
–8
–7
–6
–5
–4
–3
–2
–1
0
1
2
3
0.1
1
10
100
0.01
VO = 300mV p-p
200 METERS
300 METERS
The Schottky diodes are required to protect the AD8123 from
any AD8143 outputs that may exceed the AD8123 input limits.
The 49.9 Ω resistor limits the fault current and produces a pole
at approximately 800 MHz with the effective diode capacitance of
3 pF and the AD8123 input capacitance of 1 pF. The pole drops
the response by only 0.07 dB at 100 MHz and therefore has a
negligible effect on the signal.
When using a single 5 V supply on the driver side, the common-
mode voltage at the driver is typically midsupply, or VCM = 2.5 V.
The largest received differential video signal is approximately
700 mV p-p, and this therefore adds 175 mVPEAK to the common-
mode voltage, resulting in a worst-case peak voltage of 2.675 V
on an AD8123 input (presuming there is no ground shift between
driver and receiver). This is within the AD8123 input voltage
swing limits, and such a system works well as long as the difference
in ground potential between driver and receiver does not cause
the input voltage swing to exceed its specified limits.
Figure 33. Small Signal Frequency Response for Various Cable Lengths
POWER-DOWN
The power-down feature is intended to be used to reduce power
consumption when a particular device is not in use and does
not place the output in a high-Z state when asserted. The input
logic levels and supply current in power-down mode are presented
in the Power Supply section of Table 1.
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