參數(shù)資料
型號(hào): THS4502CDRG4
廠商: Texas Instruments, Inc.
元件分類: 運(yùn)動(dòng)控制電子
英文描述: WIDEBAND, LOW-DISTORTION FULLY DIFFERENTIAL AMPLIFIERS
中文描述: 寬帶,低失真全差動(dòng)放大器
文件頁(yè)數(shù): 27/40頁(yè)
文件大小: 609K
代理商: THS4502CDRG4
THS4502
THS4503
SLOS352D
APRIL 2002
REVISED JANUARY 2004
www.ti.com
27
As can be seen in the equation, when a higher impedance
is used, the same level of intermodulation distortion
performance results in a lower intercept point. Therefore,
it is important to comprehend the impedance seen by the
output of the fully differential amplifier when selecting a
minimum intercept point. The graphic below shows the
relationship between the strict definition of an intercept
point with a normalized, or equivalent, intercept point for
the THS4502.
Figure 105
40
30
20
15
0
10 20
30 40
f
Frequency
MHz
50 60
50
55
THIRD-ORDER OUTPUT INTERCEPT POINT
vs
FREQUENCY
60
Normalized to 200
70 80
90 100
45
35
25
Gain = 1
R
f
= 392
V
S
=
±
5 V
Tone Spacing = 200 kHz
OIP
3
R
L
= 800
Normalized to 50
O3
Comparing specifications between different device types
becomes easier when a common impedance level is
assumed. For this reason, the intercept points on the
THS4500 family of devices are reported normalized to a
50-
load impedance.
AN ANALYSIS OF NOISE IN FULLY
DIFFERENTIAL AMPLIFIERS
Noise analysis in fully differential amplifiers is analogous
to noise analysis in single-ended amplifiers. The same
concepts apply. Below, a generic circuit diagram
consisting of a voltage source, a termination resistor, two
gain setting resistors, two feedback resistors, and a fully
differential amplifier is shown, including all the relevant
noise sources. From this circuit, the noise factor (F) and
noise figure (NF) are calculated. The figures indicate the
appropriate scaling factor for each of the noise sources in
two different cases. The first case includes the termination
resistor, and the second, simplified case assumes that the
voltage source is properly terminated by the gain-setting
resistors. With these scaling factors, the amplifier
s input
noise power (N
A
) can be calculated by summing each
individual noise source with its scaling factor. The noise
delivered to the amplifier by the source (N
I
) and input noise
power are used to calculate the noise factor and noise
figure as shown in equations 23 through 27.
Figure 106. Noise Sources in a Fully
Differential Amplifier Circuit
N
i
N
A
R
g
R
f
e
g
e
f
e
s
R
s
e
n
N
o
i
ni
i
ii
R
t
e
t
N
i
S
i
N
o
S
o
+
fully-diff
amp
R
g
R
f
e
g
e
f
R
g
R
f
R
g
R
g
R
s
R
t
2 R
s
R
t
2
(e
ni
)
2
(i
ni
)
2
(i
ii
)
2
4kTR
t
2R
s
R
G
R
s
2R
s
R
g
R
s
2R
g
R
t
2R
g
2
4kTR
f
2
R
g
R
f
2
4kTR
g
2
R
g
R
g
R
s
R
t
2 R
s
R
t
2
N
A
: Fully Differential Amplifier
Noise
Source
Scale Factor
(12)
(13)
(14)
(15)
(16)
(17)
R
g2
R
g2
Figure 107. Scaling Factors for Individual Noise
Sources Assuming a Finite Value Termination
Resistor
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THS4502IDDT 制造商:TI 制造商全稱:Texas Instruments 功能描述:WIDEBAND, LOW-DISTORTION FULLY DIFFERENTIAL AMPLIFIERS
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