參數(shù)資料
型號: AD604-EVALZ
廠商: Analog Devices Inc
文件頁數(shù): 7/33頁
文件大?。?/td> 0K
描述: BOARD EVAL FOR AD604 AMP
標準包裝: 1
系列: X-AMP®
每 IC 通道數(shù): 2 - 雙
放大器類型: 可變增益
輸出類型: 單端
轉(zhuǎn)換速率: 170 V/µs
-3db帶寬: 40MHz
電流 - 輸出 / 通道: 40mA
工作溫度: -40°C ~ 85°C
電流供應(主 IC): 32mA
板類型: 完全填充
已供物品:
已用 IC / 零件: AD604
相關產(chǎn)品: AD604ARZ-RL-ND - IC AMP VGA DUAL ULN 40MA 24SOIC
AD604ANZ-ND - IC AMP VGA DUAL ULN 40MA 24DIP
AD604ARSZ-R7-ND - IC AMP VGA DUAL ULN 40MA 24SSOP
AD604ARSZ-RL-ND - IC AMP VGA DUAL ULN 40MA 24SSOP
AD604ARSZ-ND - IC AMP VGA DUAL ULN 40MA 24SSOP
AD604ARZ-ND - IC AMP VGA DUAL ULN 40MA 24SOIC
AD604AR-REEL-ND - IC AMP VGA DUAL ULN 40MA 24SOIC
AD604AR-ND - IC AMP VGA DUAL ULN 40MA 24SOIC
AD604
Rev. G | Page 14 of 32
PREAMPLIFIER
The input capability of the following single-supply DSX (2.5 ± 2 V
for a +5 V supply) limits the maximum input voltage of the
preamplifier to ±400 mV for the 14 dB gain configuration or
±200 mV for the 20 dB gain configuration.
The preamplifier gain can be programmed to 14 dB or 20 dB by
either shorting the FBK1 node to PAO1 (14 dB) or by leaving
the FBK1 node open (20 dB). These two gain settings are very
accurate because they are set by the ratio of the on-chip resistors.
Any intermediate gain can be achieved by connecting the
appropriate resistor value between PAO1 and FBK1 according
to Equation 2 and Equation 3.
()
6
5
||
7
R
V
G
EXT
IN
OUT
+
=
(2)
()
[]
() ()
6
5
6
7
6
5
6
R
G
R
G
R
EXT
+
×
×
+
×
=
(3)
Because the internal resistors have an absolute tolerance of ±20%,
the gain can be in error by as much as 0.33 dB when REXT is 30 Ω,
where it is assumed that REXT is exact.
Figure 38 shows how the preamplifier is set to gains of 14 dB,
17.5 dB, and 20 dB. The gain range of a single channel of the
AD604 is 0 dB to 48 dB when the preamplifier is set to 14 dB
(Figure 38a), 3.5 dB to 51.5 dB for a preamp gain of 17.5 dB
(Figure 38b), and 6 dB to 54 dB for the highest preamp gain of
20 dB (Figure 38c).
FBK1
PAO1
COM1
PAI1
FBK1
PAO1
COM1
PAI1
FBK1
PAO1
COM1
PAI1
R6
8
R5
32
R7
40
a. PREAMP GAIN = 14dB
b. PREAMP GAIN = 17.5dB
c. PREAMP GAIN = 20dB
R10
40
R7
40
R5
32
R6
8
R7
40
R5
32
R6
8
00
54
0-
03
8
Figure 38. Preamplifier Gain Programmability
For a preamplifier gain of 14 dB, the 3 dB small signal bandwidth
of the preamplifier is 130 MHz. When the gain is at its maximum
of 20 dB, the bandwidth is reduced by half to 65 MHz. Figure 39
shows the ac response for the three preamp gains shown in
Figure 38. Note that the gain for an REXT of 40 Ω should be
17.5 dB, but the mismatch between the internal resistors and
the external resistor causes the actual gain for this particular
preamplifier to be 17.7 dB. The 3 dB small signal bandwidth of
one complete channel of the AD604 (preamplifier and DSX) is
40 MHz and is independent of gain.
To achieve optimum specifications, power and ground manage-
ment are critical to the AD604. Large dynamic currents result
because of the low resistances needed for the desired noise
performance. Most of the difficulty is with the very low gain
setting resistors of the preamplifier that allow for a total input
referred noise, including the DSX, as low as 0.8 nV/√Hz. The
consequently large dynamic currents have to be carefully
handled to maintain performance even at large signal levels.
20
19
10
GA
IN
(
d
B
)
18
17
16
15
14
13
12
11
OPEN
SHORT
50
40
150
8
32
IN
40
100M
10M
1M
100k
FREQUENCY (Hz)
REXT
VIN
00
54
0-
03
9
Figure 39. AC Response for Preamplifier Gains of 14 dB, 17.5 dB, and 20 dB
The preamplifier uses a dual ±5 V supply to accommodate large
dynamic currents and a ground referenced input. The preamplifier
output is also ground referenced and requires a common-mode
level shift into the single-supply DSX. The two external coupling
capacitors (C1 and C2 in Figure 37) connected to the PAO1 and
+DSXx, and –DSXx, nodes and ground, respectively, perform
this function (see the AC Coupling section). In addition, they
eliminate any offset that would otherwise be introduced by the
preamplifier. It should be noted that an offset of 1 mV at the
input of the DSX is amplified by 34.4 dB (× 52.5) when the gain
control voltage is at its maximum; this equates to 52.5 mV at the
output. AC coupling is consequently required to keep the offset
from degrading the output signal range.
The gain-setting preamplifier feedback resistors are small
enough (8 Ω and 32 Ω) that even an additional 1 Ω in the
ground connection at Pin COM1 (the input common-mode
reference) seriously degrades gain accuracy and noise performance.
This node is sensitive, and careful attention is necessary to
minimize the ground impedance. All connections to the COM1
node should be as short as possible.
The preamplifier, including the gain setting resistors, has a
noise performance of 0.71 nV/√Hz and 3 pA/√Hz. Note that a
significant portion of the total input referred voltage noise is
due to the feedback resistors. The equivalent noise resistance
presented by R5 and R6 in parallel is nominally 6.4 Ω, which
contributes 0.33 nV/√Hz to the total input referred voltage noise.
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