参数资料
型号: LT5554IUH#PBF
厂商: Linear Technology
文件页数: 15/32页
文件大小: 0K
描述: IC VGA DIG CONTROL 32-QFN
标准包装: 73
应用: 可变增益(VGA)
电路数: 1
-3db带宽: 1GHz
电流 - 电源: 200mA
电压 - 电源,单路/双路(±): 4.75 V ~ 5.25 V
安装类型: 表面贴装
封装/外壳: 32-WFQFN 裸露焊盘
供应商设备封装: 32-QFN 裸露焊盘(5x5)
包装: 管件
产品目录页面: 1322 (CN2011-ZH PDF)
LT5554
22
5554f
APPLICATIONS INFORMATION
The LT5554 Noise and Linearity performance throughout
the 16dB gain range has an obvious discontinuity at every
4dB gain step. The noise gure is fairly constant from 0dB
(Maximum Gain) to –3.875dB attenuation when the gain is
decreased by lowering the amplier transconductance. And
then, the NF increases by 4dB when the input attenuator
is switched to –4dB attenuation while the amplier gain
is switched back to maximum transconductance. This
pattern repeats for each 4dB gain step change.
SECOND ORDER HARMONIC DISTORTION
Balanced differential inputs and outputs are important
for achieving excellent second order harmonic distortion
(HD2) of the LT5554. When congured in single-ended
input and output interfaces, therefore, the single-ended
to differential conversion at the input and differential to
single-ended conversion at the output will have signicant
impact on the HD2 performance.
Figure 14, for example, shows the desirable singe-ended
input and output conguration using external transformers
for the single-ended to differential conversion and differ-
ential to single-ended conversion. To assure a good HD2
performance, R5 and R6 should also be matched to better
than 1% or use these two resistors with 1% component
tolerance. In this case, the HD2 can be as good as -80dBc
when the output power is 10dBm at 140MHz.
When the single-ended input is not converted into well
balanced inputs to LT5554, the HD2 performance will
be degraded. For instance, when the T1 transformer is
improperly rotated by 90 degrees as shown in Figure 15,
the imbalance of the differential input signals will result in
14dB degradation in HD2. It is also important to split the
differential R7 resistor into two single-ended R5 and R6
resistors at the outputs to reduce the imbalance of the T2
transformer. If not, 3dB degradation in HD2 performance
can also be observed.
The HD2 performance can be further improved by mounting
a capacitor from IN+ to ground (a few pF) and a capaci-
tor from OUTto ground. For narrow band applications,
these capacitors cancels to some degree the T1 and T2
imbalance as shown in Figure 15.
For optimum HD2 performance, fully differential input and
output interfaces to the LT5554 part are recommended.
Figure 15. Not Recommended Single-Ended Input and Output
Conguration, HD2 = –63dBc at 10dBm, 140MHz
Figure 14. Recommended Single-Ended Input and Output
Conguration, HD2 = –80dBc at 10dBm, 140MHz
IN+
IN
T1
1:1
ETC1-1-13
C5
1μF
LT5554
5554 F14
OUT+
OUT
R5
68.1Ω
R6
68.1Ω
RO
400Ω
VCCO = 5V
VCC = 5V
T2
TC2-1T
C3
0.1μF
C4
0.1μF
DEC
50Ω
IN+
IN
T1
1:1
ETC1-1-13
C5
1μF
LT5554
5554 F15
OUT+
OUT
R7
134Ω
RO
400Ω
DEC
50Ω
VCCO = 5V
VCC = 5V
T2
TC2-1T
C3
0.1μF
C4
0.1μF
C1
47nF
C2
47nF
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