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參數資料
| 型號： | AD9874EB |
| 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： | 31/40頁 |
| 文件大?。?/td> | 744K |
| 代理商： | AD9874EB |
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REV. 0
AD9874
–31–
Figure 22b plots the nominal system NF with 16-bit output data
as a function of AGC in both narrow-band and wideband mode.
In wideband mode, the NF curve is virtually unchanged relative to
the 24-bit output data because the output SNR before truncation
is always less than the 96 dB SNR that 16-bit data can support.
N
15
8
14
13
12
11
10
9
SNR = 98.8dBFS
BW = 50kHz
BW = 150kHz
SNR = 83dBFS
SNR = 94.1dBFS
BW = 10kHz
SNR = 89.9dBFS
16
17
3
6
0
9
12
VGA ATTENUATION – dB
Figure 22b. Nominal System Noise Figure and Peak SNR
vs. AGCG Setting (f
IF
= 73.35 MHz, f
CLK
= 18 MSPS, and
16-bit I/Q data)
However, in narrow-band mode, where the output SNR approaches
or exceeds the SNR that can be supported with 16-bit data, the
degradation in system NF is more severe. Furthermore, if the
signal processing within the DSP adds noise at the level of an LSB,
the system noise figure can be degraded even more than Figure22b
shows. For example, this could occur in a fixed 16-bit DSP whose
code is not optimized to process the AD9874’s 16-bit data with
minimal quantization effects. To limit the quantization effects
within the AD9874, the 24-bit data undergoes noise shaping just
prior to 16-bit truncation, thus reducing the in-band quantization
noise by 5 dB (with 2 oversampling). This explains why 98.8 dBFS
SNR performance is still achievable with 16-bit data in a 10 kHz BW.
APPLICATION CONSIDERATIONS
Frequency Planning
The LO frequency (and/or ADC clock frequency) must be chosen
carefully to prevent known internally generated spurs from mixing
down along with the desired signal, thus degrading the SNR
performance. The major sources of spurs in the AD9874 are the
ADC clock and digital circuitry operating at 1/3 of
f
CLK
. Thus,
the clock frequency (
f
CLK
) is the most important variable in
determining which LO (and therefore IF) frequencies are viable.
I–80
–70
–90
–50
0
250
300
200
150
100
50
LO FREQUENCY – MHz
Figure 23a. Total In-Band Noise + Spur Power with No Signal Applied as a Function of the LO Frequency
(f
CLK
= 18 MHz and Output Signal Bandwidth of 150 kHz)
I–80
–70
–90
–50
0
250
300
LO FREQUENCY – MHz
200
150
100
50
Figure 23b. Same as Figure 23a Excluding LO Frequencies Known to Produce Large In-Band Spurs
相關PDF資料 |
PDF描述 |
|---|---|
| AD9875BSTRL | Broadband Modem Mixed-Signal Front End |
| AD9875 | Broadband Modem Mixed-Signal Front End |
| AD9875-EB | Broadband Modem Mixed-Signal Front End |
| AD9875BST | Broadband Modem Mixed-Signal Front End |
| AD9876 | Broadband Modem Mixed-Signal Front End |
相關代理商/技術參數 |
參數描述 |
|---|---|
| AD9874-EB | 制造商:Analog Devices 功能描述: |
| AD9874-EBZ | 功能描述:BOARD EVAL FOR AD9874 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:AD9874 所含物品:板 標準包裝:1 |
| AD9875 | 制造商:AD 制造商全稱:Analog Devices 功能描述:Broadband Modem Mixed-Signal Front End |
| AD9875BST | 制造商:Analog Devices 功能描述:Modem Chip Single 48-Pin LQFP 制造商:Rochester Electronics LLC 功能描述:10B BROADBAND MODEM MXFE CONVERTER - Tape and Reel |
| AD9875BSTRL | 制造商:Analog Devices 功能描述:Modem Chip Single 48-Pin LQFP T/R |
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