参数资料
型号: ADA4897-2ARMZ-R7
厂商: Analog Devices Inc
文件页数: 13/29页
文件大小: 0K
描述: IC OPAMP RR 230MHZ LP 10MSOP
标准包装: 1,000
放大器类型: 电压反馈
电路数: 2
输出类型: 满摆幅
转换速率: 120 V/µs
-3db带宽: 230MHz
电流 - 输入偏压: 11µA
电压 - 输入偏移: 28µV
电流 - 电源: 3mA
电流 - 输出 / 通道: 80mA
电压 - 电源,单路/双路(±): 3 V ~ 10 V,±1.5 V ~ 5 V
工作温度: -40°C ~ 125°C
安装类型: 表面贴装
封装/外壳: 10-TFSOP,10-MSOP(0.118",3.00mm 宽)
供应商设备封装: 10-MSOP
包装: 带卷 (TR)
Data Sheet
ADA4896-2/ADA4897-1/ADA4897-2
Rev.
| Page 19 of 28
NOISE CONSIDERATIONS
Figure 48 illustrates the primary noise contributors for the
typical gain configurations. The total rms output noise is
the root-mean-square of all the contributions.
RG
RS
iep
ien
+ vout_en –
RF
ven
4kT × RS
vn _ RS =
4kT × RG
vn _ RG =
4kT × RF
vn _ RF =
09447-
034
Figure 48. Noise Sources in Typical Connection
The output noise spectral density can be calculated by
[]
2
4
1
4
_
F
G
F
S
G
F
R
ien
kTR
R
ven
R
iep
kTRs
R
kTR
en
vout
+
+
+
=
(6)
where:
k is Boltzmann’s constant.
T is the absolute temperature (degrees Kelvin).
iep and ien represent the amplifier input current noise spectral
density (pA/√Hz).
ven is the amplifier input voltage noise spectral density (nV/√Hz).
RS is the source resistance, as shown in Figure 48.
RF and RG are the feedback network resistances, as shown in
Source resistance noise, amplifier voltage noise (ven), and the
voltage noise from the amplifier current noise (iep × RS) are all
subject to the noise gain term (1 + RF/RG). Note that with a
1 nV/√Hz input voltage noise and 2.8 pA/√Hz input current
noise, the noise contributions of the amplifier are relatively
small for source resistances from approximately 50 Ω to 700 Ω.
Figure 49 shows the total RTI noise due to the amplifier vs. the
source resistance. In addition, the value of the feedback resistors
used affects the noise. It is recommended that the value of the
feedback resistors be maintained between 250 Ω and 1 kΩ to
keep the total noise low.
50
500
NO
IS
E
(
n
V
/√
Hz
)
SOURCE RESISTANCE ()
5
0.5
50
500
5k
50k
TOTAL
AMPLIFIER NOISE
AMPLIFIER AND
RESISTOR NOISE
SOURCE
RESISTANCE NOISE
0
944
7-
0
57
Figure 49. RTI Noise vs. Source Resistance
CAPACITANCE DRIVE
Capacitance at the output of an amplifier creates a delay within the
feedback path that, if within the bandwidth of the loop, can create
excessive ringing and oscillation. The ADA4896-2/ADA4897-1/
ADA4897-2 show the most peaking at a gain of +2 (see Figure 9).
Placing a small snub resistor (RSNUB) in series with the amplifier
output and the capacitive load mitigates the problem. Figure 50
shows the effect of using a snub resistor (RSNUB) on reducing the
peaking for the worst-case frequency response (gain of +2).
Using RSNUB = 100 Ω eliminates the peaking entirely, with the
trade-off that the closed-loop gain is reduced by 0.8 dB due to
attenuation at the output. RSNUB can be adjusted from 0 Ω to
100 Ω to maintain an acceptable level of peaking and closed-
loop gain (see Figure 50).
–5
–4
–3
–2
–1
0
1
2
3
NO
RM
AL
IZ
E
D
CL
O
S
E
D
-L
O
P
G
AI
N
(
d
B)
FREQUENCY (MHz)
0.1
1
10
100
RSNUB = 50
RSNUB = 0
RSNUB = 100
ADA4896-2
RL
1k
R1
249
R2
249
CL
39pF
RSNUB
VIN
VOUT
VS = +5V
VOUT = 200mV p-p
G = +2
09
447
-05
8
Figure 50. Using a Snub Resistor to Reduce Peaking
Due to Output Capacitive Load
B
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