參數(shù)資料
型號(hào)： AD8336ACPZ-RL
廠商： Analog Devices Inc
文件頁(yè)數(shù)： 14/28頁(yè)
文件大小： 0K
描述： IC VGA GP SGL-ENDED 16-LFCSP
標(biāo)準(zhǔn)包裝： 5,000
系列： X-AMP®
類型： 可變?cè)鲆娣糯笃?br>
應(yīng)用： 信號(hào)處理
安裝類型： 表面貼裝
封裝/外殼： 16-VQFN 裸露焊盤(pán)，CSP
供應(yīng)商設(shè)備封裝： 16-LFCSP-VQ EP（4x4）
包裝： 帶卷 (TR)
配用： AD8336-EVALZ-ND - BOARD EVALUATION FOR AD8336
AD8336
Rev. C | Page 21 of 28
SETTING THE GAIN
The overall gain of the AD8336 is the sum (in decibels) or the
product (magnitude) of the preamp gain and the VGA gain.
The preamp gain is calculated as with any op amp, as seen in
the Applications Information section. It is most convenient to
think of the device gain in exponential terms (that is, in decibels)
since the VGA responds linearly in decibels with changes in
control voltage VGAIN at the gain pins.
The gain equation for the VGA is
dB
4
.
4
V
dB
50
(V)
(dB)
+
×
=
GAIN
V
Gain
VGA
where VGAIN = VGPOS VGNEG.
The gain and gain range of the VGA are both fixed at 34 dB and
60 dB, respectively; thus, the composite device gain is changed
by adjusting the preamp gain. For a preamp gain of 12 dB (4×),
the composite gain is 14 dB to +46 dB. Therefore, the calculation
for the composite gain (in decibels) is
Composite Gain
= GPRA + [VGAIN (V) × 49.9 dB/V] + 4.4 dB
For example, the midpoint gain when the preamp gain is 12 dB is
12 dB + [0 V × 49.9 dB/V] + 4.4 dB = 16.4 dB
Figure 3 is a plot of gain in decibels vs. VGAIN in millivolts, when
the preamp gain is 12 dB (4×). Note that the computed result
closely matches the plot of actual gain.
In Figure 3, the gain slope flattens at the limits of the VGAIN
input. The gain response is linear-in-dB over the center 80% of
the control range of the device. Figure 78 shows the ideal gain
characteristics for the VGA stage gain, the composite gain, and
the preamp gain.
GA
IN
(
d
B
)
40
50
30
10
0
20
–10
60
70
VGAIN (V)
FOR PREAMP GAIN = 26dB
–20
–30
FOR PREAMP GAIN = 6dB
GAIN CHARACTERISTICS
COMPOSITE GAIN
VGA STAGE GAIN
USABLE GAIN RANGE OF
AD8336
FOR PREAMP GAIN = 12dB
0.5
0.7
0.3
0.1
–0.1
–0.3
–0.5
–0.7
06
22
8-
0
78
Figure 78. Ideal Gain Characteristics of the AD8336
NOISE
The noise of the AD8336 is dependent on the value of the VGA
gain. At maximum VGAIN, the dominant noise source is the
preamp, but it shifts to the VGA as VGAIN diminishes.
The input-referred noise at the highest VGA gain and a preamp
gain of 4×, with RFB1 = 100 Ω and RFB2 = 301 Ω, is 3 nV/√Hz and
is determined by the preamp and its gain setting resistors. See
Table 4 for the noise components for the preamp.
Table 4. AD8336 Noise Components for Preamp Gain = 4×
Noise Component
Noise Voltage (nV/√Hz)
Op Amp (Gain = 4×)
2.6
RFB1 = 100 Ω
0.96
RFB2 = 301 Ω
0.55
VGA
0.77
Using the values listed in Table 4, the total noise of the AD8336
is slightly less than 3 nV/√Hz, referred to the input. Although
the input noise referred to the VGA is 3.1 nV/√Hz, the input-
referred noise at the preamp is 0.77 nV/√Hz when divided by
the preamplifier gain of 4×.
At other than maximum gain, the noise of the VGA is determined
from the output noise. The noise in the center of the gain range
is about 150 nV/√Hz. Because the gain of the fixed
-gain amplifier
that is part of the VGA is 50×, the VGA input-referred noise is
approximately 3 nV/√Hz, the same value as the preamp and VGA
combined. This is expected since the input-referred noise is the
same at the input of the attenuator at maximum gain. However,
the noise referred to the VGAI pin (the preamp output) increases
by the amount of attenuation through the ladder network. The
noise at any point along the ladder network is primarily composed
of the ladder resistance noise, the noise of the input devices, and
the feedback resistor network noise. The ladder network and
the input devices are the largest noise sources.
At minimum gain, the output noise increases slightly to about
180 nV/√Hz because of the finite structure of the X-AMP.
OFFSET VOLTAGE
Extensive cancellation circuitry included in the variable gain
amplifier section minimizes locally generated offset voltages.
However, when operated at very large values of gain, dc voltage
errors at the output can still result from small dc input voltages.
When configured for the nominal gain range of 14 dB to +46 dB,
the maximum gain is 200× and an offset of only 100 μV at the
input generates 20 mV at the output.
The primary source for dc offset errors is the preamplifier;
ac coupling between the PRAO and VGAI pins is the simplest
solution. In applications where dc coupling is essential, a
compensating current can be injected at the INPN input (Pin 5)
to cancel preamp offset. The direction of the compensating
current depends on the polarity of the offset voltage.
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參數(shù)描述
AD8336ACPZ-WP 功能描述:IC VGA GP SGL-ENDED 16-LFCSP 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(xùn)模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標(biāo)準(zhǔn)包裝:60 系列:- 類型:可變?cè)鲆娣糯笃?應(yīng)用:CATV 安裝類型:表面貼裝 封裝/外殼:20-WQFN 裸露焊盤(pán) 供應(yīng)商設(shè)備封裝:20-TQFN-EP（5x5） 包裝:托盤(pán)
AD8336-EVALZ 功能描述:BOARD EVALUATION FOR AD8336 RoHS:是 類別:編程器，開(kāi)發(fā)系統(tǒng) >> 評(píng)估板 - 運(yùn)算放大器 系列:X-AMP® 產(chǎn)品培訓(xùn)模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標(biāo)準(zhǔn)包裝:1 系列:-
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