参数资料
型号: LT1993CUD-2#TRPBF
厂商: Linear Technology
文件页数: 6/20页
文件大小: 0K
描述: IC DIFF AMP/ADC DRVR 16-QFN
标准包装: 2,500
放大器类型: 差分
电路数: 2
输出类型: 差分
转换速率: 1100 V/µs
-3db带宽: 800MHz
电流 - 输入偏压: 5µA
电压 - 输入偏移: 1000µV
电流 - 电源: 100mA
电流 - 输出 / 通道: 45mA
电压 - 电源,单路/双路(±): 4 V ~ 5.5 V,±2 V ~ 2.5 V
工作温度: 0°C ~ 70°C
安装类型: 表面贴装
封装/外壳: 16-WFQFN 裸露焊盘
供应商设备封装: 16-QFN-EP(3x3)
包装: 带卷 (TR)
LT1993-2
14
19932fa
APPLICATIO S I FOR ATIO
WU
U
Circuit Description
The LT1993-2 is a low-noise, low-distortion differential
amplier/ADC driver with:
DC to 800MHz –3dB bandwidth
Fixed gain of 2V/V (6dB) independent of RLOAD
200
Ω differential input impedance
Low output impedance
Built-in, user adjustable output ltering
Requires minimal support circuitry
Referring to the block diagram, the LT1993-2 uses a closed-
loop topology which incorporates 3 internal ampliers.
Two of the ampliers (A and B) are identical and drive
the differential outputs. The third amplier (C) is used
to set the output common mode voltage. Gain and input
impedance are set by the 200
Ω resistors in the internal
feedback network. Output impedance is low, determined
by the inherent output impedance of ampliers A and B,
and further reduced by internal feedback.
The LT1993-2 also includes built-in single-pole output
ltering. The user has the choice of using the unltered
outputs, the ltered outputs (175MHz –3dB lowpass), or
modifying the ltered outputs to alter frequency response
by adding additional components. Many lowpass and
bandpass lters are easily implemented with just one or
two additional components.
The LT1993-2 has been designed to minimize the need
for external support components such as transformers or
AC-coupling capacitors. As an ADC driver, the LT1993-2
requires no external components except for power-supply
bypass capacitors. This allows DC-coupled operation for
applications that have frequency ranges including DC.
At the outputs, the common mode voltage is set via the
VOCM pin, allowing the LT1993-2 to drive ADCs directly. No
output AC-coupling capacitors or transformers are needed.
At the inputs, signals can be differential or single-ended
with virtually no difference in performance. Furthermore,
DC levels at the inputs can be set independently of the
output common mode voltage. These input characteristics
often eliminate the need for an input transformer and/or
AC-coupling capacitors.
Input Impedance and Matching Networks
Because of the internal feedback network, calculation of
the LT1993-2’s input impedance is not straightforward
from examination of the block diagram. Furthermore, the
input impedance when driven differentially is different than
when driven single-ended. When driven differentially, the
LT1993-2’s input impedance is 200
Ω (differential); when
driven single-ended, the input impedance is 133
Ω.
For single-ended 50
Ω applications, an 80.6Ω shunt
matching resistor to ground will result in the proper input
termination (Figure 1). For differential inputs there are
several termination options. If the input source is 50
Ω
differential, then input matching can be accomplished by
either a 67
Ω shunt resistor across the inputs (Figure 3),
or a 33
Ω shunt resistor on each of the inputs to ground
(Figure 2). If additional AC gain is desired, a 1:4 impedance
ratio transformer (like the Mini-Circuits TCM4-19) can also
be used to better match impedances and to provide an ad-
ditional 6dB of gain (Figure 4). With a 1:4 impedance ratio
transformer, ideal matching impedance at the transformer
output is 200
Ω, so no termination resistors are required
to match the LT1993-2’s 200
Ω input impedance.
19932 F01
IF IN
0.1
F
LT1993-2
–INA
–INB
–OUT
+OUT
8
5
+INB
+INA
14
13
15
80.6
ZIN = 50
SINGLE-ENDED
16
Figure 1. Input Termination for Single-Ended 50
Ω
Input Impedance
Figure 2. Input Termination for Differential 50
Ω Input Impedance
19932 F02
IF IN
IF IN+
LT1993-2
–INA
–INB
–OUT
+OUT
8
5
+INB
+INA
14
13
15
33
ZIN = 50
DIFFERENTIAL
16
33
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