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| 型號： | AD8335ACPZ-REEL |
| 廠商： | Analog Devices Inc |
| 文件頁數(shù)： | 15/28頁 |
| 文件大小： | 0K |
| 描述： | IC AMP VGA QUAD 64LFCSP |
| 產(chǎn)品變化通告： | AD8335 Metal Mask Change 12/Jul/2010 |
| 標準包裝： | 2,500 |
| 系列： | X-AMP® |
| 類型： | 可變增益放大器 |
| 應(yīng)用： | 信號處理 |
| 安裝類型： | 表面貼裝 |
| 封裝/外殼： | 64-VFQFN 裸露焊盤，CSP |
| 供應(yīng)商設(shè)備封裝： | 64-LFCSP-VQ（9x9） |
| 包裝： | 帶卷 (TR) |
| 配用： | AD8335-EVALZ-ND - BOARD EVALUATION FOR AD8335 |
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AD8335
Data Sheet
Rev. B | Page 22 of 28
The preamp PMD pins must be capacitively coupled to ground.
Although the preamplifier is a differential design, the PMD pins
are the internal input bias nodes and are made available for
bypassing only. Do not use these pins as signal inputs.
The PIPx inputs must be capacitively coupled from the signal
source because they have a nominal dc level of more than half
the supply voltage. AC coupling capacitors throughout the circuit
should be as large as possible for the application. Although 0.1 μF
capacitors are shown in Figure 58 (and used in most positions
in the evaluation board), values of these capacitors should be
determined by the application. Capacitors used for coupling
PMDx and PIPx pins should be the same value.
When synthesizing low values of RIN, the bandwidth of the
preamplifier produces some peaking at the high end of the
frequency response. The optional series RSHx/CSHx network shown
in Figure 58 flattens the response (see Figure 55). With a 50 Ω
source, the resistor and capacitor values should be 49.9 Ω and
22 pF. For RS values greater than 100 Ω, the network is not needed.
The circuit is stable in either scenario.
The starred capacitors in Figure 58 (*) on the VGNx pins can be
removed when faster gain control signals are required.
INPUT OVERDRIVE
Excellent overload behavior is of primary importance in ultra-
sound. Both the preamplifier and VGA have built-in overdrive
protection and quickly recover after an overload event.
Input Overload Protection
As with any amplifier, voltage clamping prior to the inputs is
highly recommended if the application is subject to high
transient voltages.
A block diagram of a simplified ultrasound transducer interface
is shown in Figure 59. A common transducer element serves the
dual functions of transmit and receive of ultrasound energy. During
the transmit phase, high voltage pulses are applied to the ceramic
elements. A typical T/R (transmit/receive) switch may consist of
four high voltage diodes in a bridge configuration. Although they
ideally block transmit pulses from the sensitive receiver input,
diode characteristics are not ideal, and resulting leakage
transients impinging on the PIPx inputs can be problematic.
Because ultrasound is a pulse system, and time-of-flight is used to
determine depth, quick recovery from input overloads is essential.
Overload can occur in the preamp and the VGA. Immediately
following a transmit pulse, the typical VGA gains are low, and
the PrA is subject to overload from T/R switch leakage. With
increasing gain, the VGA can become overloaded from strong
echoes that occur with near field echoes and acoustically dense
materials, such as bone.
Figure 59 illustrates an external overload protection scheme. A
pair of back-to-back Schottky diodes is installed prior to installing
the ac-coupling capacitors. Although the BAS40 is shown, many
types are available and merit investigation by the user. With such
diodes, clamping levels of ±0.5 V or less greatly enhance the
system overload performance.
PrA
18dB
Rs
TRANSDUCER
–HV
BAS40-04
PMDx
PIPx
PONx
POPx
OPTIONAL
SCHOTTKY
OVERLOAD
CLAMP
RFB
3
2
1
+HV
04
97
6-
0
57
Figure 59. Input Overload Protection
LOGIC INPUTS
The EN12 and EN34 enable pins, the SP12 and SP34 preamp
shutdown pins, and the HL12 and HL34 high/low pins are all
logic inputs of the AD8335. The enable inputs turn on and off
each of the corresponding pairs of channels; the preamp shutdown
pins do the same for the preamplifiers only; inputs HL12 and
HL34 set the high/low gain for Channel 1 and Channel 2, and
Channel 3 and Channel 4, respectively.
Shutting down the preamplifiers allows use of the VGAs alone,
while reducing power consumption. The VGAs cannot be shut
down independently. The SPxx (shutdown preamp) pins are
logic high; thus, the pins are grounded to enable the preamplifiers.
The pins can be enabled by connecting to the supply or to ground
for fixed enable or disable, or to the output of a logic device. Be
sure to check the data sheet of the device for voltage and current
requirements.
COMMON-MODE PINS
The common-mode VCMx pins are provided for bypassing the
internal common-mode reference for each channel to ground.
They require a capacitor at each of the four pins and can neither
be connected together nor driven by an external source.
DRIVING ADCs
The AD8335 VGA is designed to drive 10-bit and 12-bit ADCs
with minimal extra components. Because the AD8335 is a single
supply 5 V part and many of the newest ADCs operate from a 3 V
supply, dissimilar common-mode voltages exist between the VGA
output and the ADC input. This level shift is most easily accom-
modated by ac coupling, especially if the signal is filtered, as is
the case in most ultrasound and communications applications.
When an antialiasing filter (AAF) is called for, it is advantageous
to implement a differential configuration. A fully differential
AAF requires approximately 1.5 times the number of components
than a single-ended filter, because the components that in the
single-ended case are tied to ground, now connect across the
differential signal path. Although the series components double,
the component count for the differential filter is more economical
when compared to simply building a pair of single-ended filters
requiring twice as many components.
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| AD8335ACPZ-REEL7 | 功能描述:IC AMP VGA QUAD 64LFCSP RoHS:是 類別:集成電路 (IC) >> 線性 - 放大器 - 專用 系列:X-AMP® 產(chǎn)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(yīng)用:CATV 安裝類型:表面貼裝 封裝/外殼:20-WQFN 裸露焊盤 供應(yīng)商設(shè)備封裝:20-TQFN-EP（5x5） 包裝:托盤 |
| AD8335EVAL | 制造商:Analog Devices 功能描述:EVAL BOARD ((NS)) |
| AD8335-EVAL | 制造商:AD 制造商全稱:Analog Devices 功能描述:Quad Low Noise, Low Cost Variable Gain Amplifier |
| AD8335-EVALZ | 功能描述:BOARD EVALUATION FOR AD8335 RoHS:是 類別:編程器，開發(fā)系統(tǒng) >> 評估板 - 運算放大器 系列:X-AMP® 產(chǎn)品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:1 系列:- |
| AD8336 | 制造商:AD 制造商全稱:Analog Devices 功能描述:General-Purpose, −55 to +125, Wide Bandwidth, DC-Coupled VGA |
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