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參數(shù)資料
| 型號： | AD9879BSZ |
| 廠商： | Analog Devices Inc |
| 文件頁數(shù)： | 17/32頁 |
| 文件大?。?/td> | 0K |
| 描述： | IC PROCESSOR FRONT END 100MQFP |
| 標準包裝： | 1 |
| 位數(shù)： | 12 |
| 通道數(shù)： | 5 |
| 功率（瓦特）： | 587mW |
| 電壓 - 電源，模擬： | 3.3V |
| 電壓 - 電源，數(shù)字： | 3.3V |
| 封裝/外殼： | 100-BQFP |
| 供應(yīng)商設(shè)備封裝： | 100-MQFP（14x20） |
| 包裝： | 托盤 |
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AD9879
Rev. A | Page 24 of 32
Tx SIGNAL LEVEL CONSIDERATIONS
The quadrature modulator introduces a maximum gain of 3 dB
in signal level. To visualize this, assume that both the I data and
Q data are fixed at the maximum possible digital value, x. The
output of the modulator, z is then:
z = [x cos(ωt) – x sin(ωt)]
(17)
O
XZ
X
I
02773-017
Figure 17. 16-Quadrature Modulation
It can be shown that |z| assumes a maximum value of
()
(
dB
3
2
+
=
+
=
of
gain
a
x
z
)
(18)
However, if the same number of bits are used to represent the |z|
values, as is used to represent the x values, an overflow occurs.
To prevent this possibility, an effective 3 dB attenuation is
internally implemented on the I and Q data path.
(
)
(
x
z
=
+
=
2
/
1
2
/
1
)
(19)
3
LOW-PASS
FILTER
TX
AD832x
AD9879
CA
75
VARIABLE GAIN
CABLE DRIVER
AMPLIFIER
CA_EN
CA_DATA
CA_CLK
DAC
02773-018
Figure 18. 16-Quadrature Modulation
The following example assumes a PK/rms level of 10 dB:
Maximum Symbol Component Input Value =
(20)
±(2,047 LSBs 0.2 dB) = ±2,000 LSBs
Maximum Complex Input RMS Value =
(21)
2,000 LSBs + 6 dB Pk/rms (dB) = 1,265 LSBs rms
The maximum complex input rms value calculation uses both
I and Q symbol components that add a factor of 2 (6 dB) to the
formula.
Table 11 shows typical I-Q input test signals with amplitude
levels related to 12-bit full scale (FS).
Tx THROUGHPUT AND LATENCY
Data inputs impact the output fairly quickly but remain
effective due to the filter characteristics of the AD9879. Data
transmit latency through the AD9879 is easiest to describe in
terms of fSYSCLK clock cycles (4 fMCLK). The numbers quoted are
when an effect is first seen after an input value changes.
Latency of I/Q data entering the data assembler (AD9879 input)
to the DAC output is 119 fSYSCLK clock cycles (29.75 fMCLK cycles).
DC values applied to the data assembler input takes up to 176
fSYSCLK clock cycles (44 fMCLK cycles) to propagate and settle at the
DAC output.
Frequency hopping is accomplished via changing the PROFILE
input pin. The time required to switch from one frequency to
another is less than 232 fSYSCLK cycles (58.5 fMCLK cycles).
Table 11. I–Q Input Test Signals
Analog Output
Digital Input
Input Level
Modulator Output Level
Single Tone (fC – f)
I = cos(f)
FS – 0.2 dB
FS – 3.0 dB
Q = cos(f + 90°) = sin(f)
FS – 0.2 dB
Single Tone (fC + f)
I = cos(f)
FS – 0.2 dB
FS – 3.0 dB
Q = cos(f + 270°) = +sin(f)
FS – 0.2 dB
Dual Tone (fC ± f)
I = cos(f)
FS – 0.2 dB
FS
Q = cos(f + 180°) = cos(f) or Q = +cos(f)
FS – 0.2 dB
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