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參數資料
| 型號： | AD9866BCP |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | 通信及網絡 |
| 英文描述： | Broadband Modem Mixed Signal Front End |
| 中文描述： | SPECIALTY TELECOM CIRCUIT, QCC64 |
| 封裝： | MO-220-VMMD, LFCSP-64 |
| 文件頁數： | 29/48頁 |
| 文件大小： | 1647K |
| 代理商： | AD9866BCP |
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AD9866
Applications demanding the highest spectral performance
and/or lowest power consumption can use the TxDAC output
directly. The TxDAC is capable of delivering a peak signal
power-up to 10 dBm while maintaining respectable linearity
performance, as shown in Figure 27 through Figure 38. For
power-sensitive applications requiring the highest Tx power
efficiency, the TxDAC’s full-scale current output can be reduced
to as low as 2 mA and its load resistors sized to provide a
suitable voltage swing that can be amplified by a low power op-
amp-based driver.
Rev. 0 | Page 29 of 48
Most applications requiring higher peak signal powers (up to
23 dBm) should consider using the IAMP. The IAMP can be
configured as a current source for loads having a well defined
impedance (50 or 75 systems) or a voltage source (with the
addition of a pair of npn transistors) for poorly defined loads
having varying impedance (such as power lines).
Figure 62 shows the equivalent schematic of the TxDAC and
IAMP. The TxDAC provides a differential current output
appearing at IOUTP+ and IOUTP. It can be modeled as a
differential current source generating a signal-dependent ac
current, when I
S
has a peak current of I along with two dc
current sources, sourcing
a standing current equal to I. The full-
scale output current, IOUTFS, is equal to the sum of these
standing current sources (IOUTFS = 2*I).
0
N
I
N
I
G
I
G
I
I
I
I
I
±
I
S
I
I
TxDAC
REFADJ
REFIO
IOUTP+
IOUTP–
I +
I
I –
I
I
OFF1
R
SET
0.1
μ
F
I
OFF1
I
OFF2
xG
xG
xN
xN
I
OFF2
IAMP
Figure 62. Equivalent Schematic of TxDAC and IAMP
The value of I is determined by the R
SET
value at the REFADJ
pin along with the Tx path’s digital attenuation setting. With
0 dB attenuation, the value of I is
)
/
23
.
16
SET
R
I
=
Equation 1.
For example, an
R
SET
value of 1.96 k results in I equal to
10.0 mA with IOUTFS equal to 20.0 mA. Note that the REFIO
pin provides a nominal band gap reference voltage of 1.23 V
and should be decoupled to analog ground via a 0.1 μF
capacitor.
The differential current output of the TxDAC is always con-
nected to the IOUTP pins, but can be directed to the IAMP by
setting Bit 0 of Reg 0x0E. As a result, the IOUTP pins
must
remain completely open, if the IAMP is to be used. The IAMP
contains two sets of current mirrors that are used to replicate
the TxDAC’s current output with a selectable gain. The first set
of current mirrors is designated as the primary path, providing
a gain factor of N that is programmable from 0 to 4 in steps of 1
via Bits 2:0 of Reg. 0x10 with a default setting of N = 4. Bit 7 of
this register
must
be set to overwrite the default settings of this
register. This differential path exhibits the best linearity
performance (see Figure 42) and is available at the IOUTN+
and IOUTN pins. The maximum peak current per output is
100 mA and occurs when the TxDAC’s standing current, I, is set
for 12.5 mA (IOUTFS = 25 mA).
The second set of current mirrors is designated as the secon-
dary path providing a gain factor of G that is programmable
from 0 to 36 via Bits 6:4 of Reg. 0x10 and Bits 6:0 of Reg. 0x11
with a default setting of G = 12. This differential path is
intended to be used in the voltage mode configuration to bias
the external
npn
transistors, because it exhibits degraded
linearity performance (see Figure 43) relative to the primary
path . It is capable of sinking up to 180 mA of peak current into
either its IOUTG+ or IOUTG pins. The secondary path
actually consists of 3 gain stages (G1, G2, and G3), which are
individually programmable as shown in Table 19. While many
permutations may exist to provide a fixed gain of G, the
linearity performance of a secondary path remains relatively
independent of the various individual gain settings that are
possible to achieve a particular overall gain factor.
Both sets of mirrors sink
current, because they originate from
NMOS devices. Therefore, each output pin requires a dc current
path to a positive supply. Although the voltage output of each
output pin can swing between 0.5 and 7 V, optimum ac
performance is typically achieved by limiting the ac voltage
swing with a dc bias voltage set between 4 to 5 V. Lastly, both the
standing current, I, and the ac current, I
S
, from the TxDAC are
amplified by the gain factor (N and G) with the total standing
current drawn from the positive supply being equal to
I
G
N
+
)
(
2
Programmable current sources I
OFF1
and I
OFF2
via Reg. 0x12 can
be used to improve the primary and secondary path mirrors’
linearity performance under certain conditions by increasing
their signal-to-standing current ratio. This feature provides a
marginal improvement in distortion performance under large
signal conditions when the peak ac current of the reconstructed
waveform frequently approaches the dc standing current within
the TxDAC (0 to 1 dBFS sine wave) causing the internal
mirrors to turn off. However, the improvement in distortion
performance diminishes as the crest factor (peak-to-rms ratio)
of the ac signal increases. Most applications can disable these
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相關代理商/技術參數 |
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| AD9866BCPRL | 制造商:Analog Devices 功能描述:Mixed Signal Front End 64-Pin LFCSP EP T/R |
| AD9866BCPZ | 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 |
| AD9866BCPZRL | 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 |
| AD9866CHIPS | 制造商:AD 制造商全稱:Analog Devices 功能描述:Broadband Modem Mixed Signal Front End |
| AD9866-EB | 制造商:Analog Devices 功能描述: 制造商:Analog Devices 功能描述:12B MXFE CONVERTER FOR BROADBAND MODEMS - Bulk |
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