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參數資料
| 型號： | AD9864-EB |
| 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： | 27/44頁 |
| 文件大小： | 1984K |
| 代理商： | AD9864-EB |
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AD9864
(
)
[
]
C
L
f
CLK
×
×
π
×
=
2
2
/
8
TO DIGITAL
FILTER
SC
RESO-
NATOR
NINE-
LEVEL
FLASH
ESL
GAIN
CONTROL
MIXER
OUTPUT
EXTERNAL
LC
f
CLK
= 13 MSPS TO 26 MSPS
MXOP
MXON
IF2P
IF2N
RC
RESO-
NATOR
DAC1
0
For example, at
f
CLK
= 18 MHz and L = 10 μH, a capacitance of
250 pF is needed. However, in order to accommodate an induc-
tor tolerance of ±10%, the tank capacitance must be adjustable
from 227 pF to 278 pF. Selecting an external capacitor of 180 pF
ensures that even with a 10% tolerance and stray capacitances
as high as 30 pF, the total capacitance will be less than the
minimum value needed by the tank. Extra capacitance is sup-
plied by the AD9864’s on-chip programmable capacitor array.
Since the programming range of the capacitor array is at least
160 pF, the AD9864 has plenty of range to make up for the tol-
erances of low cost external components. Note that if
f
CLK
is
increased by a factor of 1.44 MHz to 26 MHz so that
f
CLK
/8
becomes 3.25 MHz, reducing
L
and
C
by approximately the
same factor (i.e.,
L
= 6.9 μH and
C
= 120 pF) still satisfies the
requirements stated above.
Figure 46. Equivalent Circuit of Sixth Order Band-Pass Σ- Modulator
Figure 47 shows the measured power spectral density measured at
the output of the undecimated band-pass Σ- modulator. Note
that the wide dynamic range achieved at the center frequency,
f
CLK
/8, is achieved once the LC and RC resonators of the Σ-
modulator have been successfully tuned. The out-of-band noise is
removed by the decimation filters following quadrature mixer.
A 16 dB step attenuator is also included within the LNA/mixer
circuitry to prevent large signals (i.e., > –18 dBm) from over-
driving the Σ- modulator. In such instances, the Σ- modula-
tor will become unstable, thus severely desensitizing the
receiver. The 16 dB step attenuator can be invoked by setting
the ATTEN bit (Register 0x03, Bit 7), causing the mixer gain to
be reduced by 16 dB. The 16 dB step attenuator could be used
in applications in which a potential target or blocker signal
could exceed the IF input clip point. Although the LNA will be
driven into compression, it may still be possible to recover the
desired signal if it is FM. Refer to Table 14 to see the gain com-
pression characteristics of the LNA and mixer with the 16 dB
attenuator enabled.
Table 14. SPI Registers Associated with LNA/Mixer
Address
(Hex)
Breakdown
Width
0x00
(7:0)
8
0x03
(7)
1
0
0
–10
–20
–30
–50
d
–40
FREQUENCY (MHz)
–60
–70
–80
–90
–100
1
2
3
4
5
6
7
8
9
–2dBFS OUTPUT
f
= 18MHz
NBW = 3.3kHz
0
Bit
Default
Value
0xFF
0
Name
STBY
ATTEN
Figure 47. Measured Undecimated Spectral Output of Σ-
Modulator ADC with f
CLK
= 18 MSPS and Noise Bandwidth of 3.3 kHz
The signal transfer function of the AD9864 possesses inherent
anti-alias filtering by virtue of the continuous-time portions of
the loop filter in the band-pass Σ- modulator. Figure 48 illus-
trates this property by plotting the nominal signal transfer
function of the ADC for frequencies up to 2
f
CLK
. The notches
that naturally occur for all frequencies that alias to the
f
CLK
/8
pass band are clearly visible. Even at the widest bandwidth set-
ting, the notches are deep enough to provide greater than 80 dB
of alias protection. Thus, the wideband IF filtering require-
ments preceding the AD9864 will be determined mostly by the
mixer’s image band, which is offset from the desired IF input
frequency by
f
CLK
/4 (i.e., 2 ×
f
CLK
/8) rather than any aliasing
associated with the ADC.
BAND-PASS ∑- ADC
The ADC of the AD9864 is shown in Figure 46. The ADC con-
tains a sixth order multibit band-pass Σ- modulator that
achieves very high instantaneous dynamic range over a narrow
frequency band. The loop filter of the band-pass Σ- modulator
consists of two continuous-time resonators followed by a discrete
time resonator, with each resonator stage contributing a pair of
complex poles. The first resonator is an external LC tank, while
the second is an on-chip active RC filter. The output of the LC
resonator is ac-coupled to the second resonator input via 100 pF
capacitors. The center frequencies of these two continuous-time
resonators must be tuned to f
CLK
/8
for the ADC to function prop-
erly. The center frequency of the discrete-time resonator auto-
matically scales with f
CLK
, thus no tuning is required.
Rev. 0 | Page 27 of 44
相關PDF資料 |
PDF描述 |
|---|---|
| AD9864BCPZ | IF Digitizing Subsystem |
| AD9864BCPZRL | IF Digitizing Subsystem |
| AD9866BCPRL | Broadband Modem Mixed Signal Front End |
| AD9866CHIPS | Broadband Modem Mixed Signal Front End |
| AD9866 | Broadband Modem Mixed Signal Front End |
相關代理商/技術參數 |
參數描述 |
|---|---|
| AD9864-EBZ | 功能描述:BOARD EVAL FOR AD9864 制造商:analog devices inc. 系列:- 零件狀態:有效 類型:數字轉換器 頻率:10MHz ~ 300MHz 配套使用產品/相關產品:AD9864 所含物品:板 標準包裝:1 |
| AD9865 | 制造商:AD 制造商全稱:Analog Devices 功能描述:Broadband Modem Mixed-Signal Front End |
| AD9865BCP | 制造商:Analog Devices 功能描述:Mixed Signal Front End 64-Pin LFCSP EP 制造商:Analog Devices 功能描述:MIXED SGNL FRONT END 64LFCSP EP - Trays 制造商:Analog Devices 功能描述:10BIT MIXED SIGNAL CONVERTER 9865 |
| AD9865BCPRL | 制造商:Analog Devices 功能描述:Mixed Signal Front End 64-Pin LFCSP EP T/R |
| AD9865BCPZ | 功能描述:IC PROCESSOR FRONT END 64LFCSP RoHS:是 類別:RF/IF 和 RFID >> RF 前端 (LNA + PA) 系列:- 產品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:250 系列:- RF 型:GPS 頻率:1575.42MHz 特點:- 封裝/外殼:48-TQFP 裸露焊盤 供應商設備封裝:48-TQFP 裸露焊盤（7x7） 包裝:托盤 |
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