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參數資料
| 型號： | AD9870EB |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | IF Digitizing Subsystem |
| 中文描述： | 中頻數字化子系統 |
| 文件頁數： | 12/20頁 |
| 文件大小： | 233K |
| 代理商： | AD9870EB |
REV. 0
AD9870
–12–
IF1 LNA/MIXER
The AD9870 contains a single-ended LNA followed by “Gilbert-
type” active mixer as shown in Figure 7a. The mixer’s differential
LO port is driven by an LO buffer stage which can be driven
single-ended or differential. The LO signal level can range from
0.3 V p-p to 1.0 V p-p with negligible effect on performance.
The input impedance at the IFIN pin is 360
2 pF (
±
20%)
and has no significant variation with respect to the programmable
bias settings. Figure 7b. shows the S11 parameters of the AD9870
with the following LNA/Mixer bias setting: LNAB = 3, MIXB = 3.
R
GAIN
R
F
R
IN
= 360
R
BIAS
LNA GAIN = 15 dB
180
180
MIXER GAIN =
–
5 dB
LO INPUT =
0.3 TO 1.0 V p
–
p
DC SERVO
LOOP
MULTI-TANH
V
–
I STAGE
VCML
Figure 7a. Simplified Schematic of AD9870’s LNA/Mixer
10
25
50
100
200 400
J10
–
J10
J25
–
J25
J50
–
J50
J100
–
J100
J200
–
J200
J400
–
J400
0
323
–
J105
AT 73.35 MHz
255
–
J163
AT 140 MHz
166
–
J177
AT 240 MHz
Figure 7b. Input Impedance (i.e. S11) of the AD9870’s
IF1 Input
Both the LNA and mixer have four programmable bias settings
so that current consumption can be minimized for a given appli-
cation. Figures 7c, 7d, and 7e show how the LNA and mixer’s
noise figure (NF), linearity (IIP3), conversion gain, current
consumption and frequency response are all affected for a given
LNA/Mixer bias setting. The measurements were taken at an IF
= 73.35 MHz, an LO = 71.1 MHz, and supplies set to 3.0 V.
Note, since the current consumption of the LNA/Mixer portion
of the IC can be reduced by only 5 mA at most relative to the
nominal current consumption of the entire IC in the high IIP3
mode (i.e., 42 mA), most applications will benefit with the
AD9870’s LNA/Mixer configured for the high bias mode (i.e.,
LNAB = 3, MIXB = 3 for SPI Port Register 1).
LNA-MIXER POWER BIAS SETTING
12
0
–
0
d
11
10
9
8
7
6
0
–
1 0
–
2 0
–
3 1
–
0 1
–
1 1
–
2 1
–
3 2
–
0 2
–
1 2
–
2 2
–
3 3
–
0 3
–
1 3
–
2 3
–
3
CONVERSION
GAIN
NOISE
FIGURE
Figure 7c. LNA/Mixer Noise Figure and Conversion Gain
vs. Bias Setting
LNA-MIXER POWER BIAS SETTING
5
0
–
0
I
–
0
–
5
–
10
–
15
–
20
–
25
0
–
1 0
–
2 0
–
3 1
–
0 1
–
1 1
–
2 1
–
3 2
–
0 2
–
1 2
–
2 2
–
3 3
–
0 3
–
1 3
–
2 3
–
3
LNA
–
MIXER
CURRENT
IIP3
C
–
9
8
7
6
5
4
3
2
1
0
Figure 7d. LNA/Mixer IIP3 and Current Consumption vs.
Bias Setting
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