```AN-827

One Technology Way • P.O. Box 9106 • Norwood, MA 02062-9106, U.S.A. • Tel: 781.329.4700 • Fax: 781.461.3113 • www.analog.com

HOLD SWITCH
INTERNAL
INPUT
CLOCK
AMP
C
AIN
INPUT
SWITCH
ESD
GND
R
ESD
BPF
SAMPLING
CAP
SAMPLING
SWITCHES
INTERNAL
SAMPLE
CLOCK
~AIN
AV CC
V BIAS
INPUT
SWITCH
SHA
n
SAMPLING
CAP
V BIAS
INTERNAL
INPUT
CLOCK
HOLD SWITCH

Rev. 0 | Page 1 of 8
05012-001
AV CC
AN-827
20
180
18
160
16
140
14
120
12
REAL Z
HOLD MODE
100
10
80
IMAG Z
TRACK MODE
REAL Z
TRACK MODE
60
8
6
40
4
IMAG Z HOLD MODE
20
0
0
100
200
300
400

IMAGINARY IMPEDANCE (pF)
200

YIN = Z IN −1 = (R + jX ) −1
2
500
600
700
800
900
0
1000
(1)

MathCAD TM ， 甚 至 最 新 版 本 的 电 子 表 格 计 算 器 ， 如
Microsoft® Excel, 也可用下面的公式求解：
(R + jX ) −1 =
05012-002
REAL IMPEDANCE (Ω )

(2)

R − jX
R − jX
1
= 2
= G + jB
R + jX R − jX R + X 2
G=
R

R2 + X 2
B=
−X

R + X2
2

R EQ =
1 R2 + X 2
=
G
R
(3)
1
−X
2
ω R + X2
(4)

C EQ =

Rev. 0 | Page 2 of 8
AN-827

−j
1
=
jωL
ωL
(5)

FS > 2 × FBW
(8)
AMPLITUDE
20MHz

G + jB = (0.77 + j3.5) mΩ−1，并联RC等效电阻为G−1 = (0.77 ×
10-3) = 1300 Ω，等效电容为(B/ω) = (3.5 × 10-3)/ (2πf) = 4 pF。

NYQUIST ZONE 1
0
FS
80MHz
FREQUENCY
NYQUIST ZONE 2
NYQUIST ZONE 3

(1/ωB) = (2πf × 3.5 × 10−3)−1 = 322 nH
0.5FS
40MHz
140MHz
(6)
NYQUIST ZONE 4

1.5FS
120MHz
05012-003
RE Q//CEQ//LP = ((1300 Ω−1 + (j2πfCEQ) + ( j2πfLP)−1)−1 = 1300 Ω (7)
2FS
160MHz
IF采样与奈奎斯特因素

0 FS至0.5 FS范围内的FFT绘图。所以，若信号频率高于0.5 FS，

Seminar”)：

(SNR)也更好。在某些情况下，这种设计还可提升无杂散

Rev. 0 | Page 3 of 8
AN-827

Nuhertz Technologies的Filter Free 4.0或Agilent Technologies推出

AMPLITUDE
2FS–F1
F1
F2
3FS–F2
IF
DYNAMIC
RANGE
IMAGE
IMAGE
IMAGE
NYQUIST ZONE 1
NYQUIST ZONE 2
NYQUIST ZONE 3
0.5FS
40MHz
FS
80MHz
NYQUIST ZONE 4
1.5FS
120MHz

Rev. 0 | Page 4 of 8
2FS
160MHz
05012-004
FREQUENCY
0
AN-827

5 (d)所示。印刷电路板寄生效应的建模对于最佳L值和C值
RS
rS = ___ = 0.125
RL
VS
VS
L3
0.40H
C2
7.708F
RS
___
= 60Ω
2
70nH
BALANCED
CONFIGURATION
RS
___
= 60Ω
2
70nH
C4
6.987F
(a)
rL = 1
fC = 1Hz
140nH
DENORMALIZED
SINGLE-ENDED
EQUIVALENT
VS

L1
0.21H
NORMALIZED
SINGLE-ENDED
EQUIVALENT
RS = 120Ω

265nH
14.2pF
12.9pF
RL = 600Ω
(b)
fC = 144MHz
132.5nH
14.2pF
12.9pF
RL = 600Ω
(c)
132.5nH
1.21kΩ
180pF 68nH
15pF
120nH
12pF
10Ω 180pF
68nH
~120Ω
120nH
12-BIT
80MSPS
270nH
DIGITAL VGA
1.21kΩ 1.21kΩ
~600Ω
(d)
(59-j270)Ω

Rev. 0 | Page 5 of 8
05012-005
10Ω
1.21kΩ
AN-827

6 dB，同时SFDR提高了10 dB以上。
0
BEFORE:
INPUT = 46MHz
@ –6dBFS
NOISE FLOOR
@ –106.3dBFS
THD = –82.1dBc
SFDR = 79.4dBc
–10
–20
–30
–40
–50
XXX (X)

–60
–70
–80
+
–90 4
3 5
–100
0
BEFORE:
–10 INPUT = –1dBFS @ 139MHz
NOISE FLOOR @ –85.1dBFS
–20 THD = –56dBc
SFDR = 47dBc
–30
–110
–120
–130
0
2.5
5.0
7.5 10.0 12.5 15.0 17.5 20.0 22.5 25.0 27.5 30.0
–40
FREQUENCY (MHz)
+
3
–60
–70
0
2
4
5
–80
6
–20
–30
–90
–40
–100
–50
XXX (X)
–110
–120
–130
0
5
10
15
20
25
30
–60
–70
40
35
–80
FREQUENCY (MHz)
–90
AFTER:
–10 INPUT = –1dBFS @ 139MHz
NOISE FLOOR @ –93.6dBFS
–20 THD = –66dBc
SFDR = 70dBc
–30
5
+ 26
–110
–120
–130
–40
0
2.5
5.0
7.5 10.0 12.5 15.0 17.5 20.0 22.5 25.0 27.5 30.0
FREQUENCY (MHz)
–50
XXX (X)
3
–100 4
0

–60
–70
2
3
4
–80

6
5
–90
–100
–110
0
5
10
15
20
25
FREQUENCY (MHz)
30
35
40
05012-006
–120
–130
AFTER:
INPUT = 46MHz
@ –6dBFS
NOISE FLOOR
@ –112.5dBFS
THD = –86.0dBc
SFDR = 89.9dBc
–10
05012-007
XXX (X)
–50
2
6

Rev. 0 | Page 6 of 8
AN-827

•
Chapter 4, High Speed Design Seminar, Walt Kester, Editor
•
Filter Free 4.0, Nuhertz Technologies—online filter design
software package
•
MS Excel
•
MATLAB
•
•
RF Circuit Design, Chris Bowick, page 66 to page 97
•
AN-742, Frequency Response of Switched-Capacitor