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參數資料
| 型號： | AD9957 |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | 1 GSPS Quadrature Digital Upconverter with 18-Bit IQ Data Path and 14-Bit DAC |
| 中文描述： | 1 GSPS的正交數字上變頻器與18位智商數據路徑和14位DAC |
| 文件頁數： | 37/60頁 |
| 文件大?。?/td> | 840K |
| 代理商： | AD9957 |
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AD9957
Table 10. OSK Amplitude Step Size
ASF<1:0>
00
01
10
11
Rev. 0 | Page 37 of 60
Amplitude Step Size
1
2
4
8
As mentioned earlier, the step interval is controlled by a 16-bit
programmable timer. Normally, this timer is loaded with the
programmed timing value whenever the timer expires, thus
initiating a new timing cycle. However, three events cause the
timer to have its timing value reloaded prior to the timer
expiring. One such event is when the select auto-OSK bit is
transitioned from a Logic 0 state to a Logic 1 state followed by
an I/O update. A second such event is a change of state in the
OSK pin. The third event is dependent on the status of the Load
ARR @ I/O Update bit. If this bit is Logic 0, then no action occurs,
otherwise, when the I/O_UPDATE pin is asserted (or a profile
change occurs), the timer resets to its initial starting point.
PROFILES
Each of the three operating modes of the AD9957 support the
use of profiles, which consist of a group of registers containing
pertinent operating parameters for a particular operating mode.
Profiles enable rapid switching between parameter sets. Profile
parameters are programmed via the serial I/O port. Once
programmed, a specific profile is activated by means of three
external pins (PROFILE<2:0>). A particular profile is activated
by providing the appropriate logic levels to the profile control
pins per the settings listed in Table 11.
Table 11. Profile Control Pins
PROFILE<2:0>
000
001
010
011
100
101
110
111
Active Profile
0
1
2
3
4
5
6
7
Consider an application of basic two-tone frequency shift
keying (FSK) where binary data is transmitted by selecting
between two different frequencies: a mark frequency (Logic 1)
and a space frequency (Logic 0). To accommodate FSK, the
Profile 0 register is programmed with the appropriate frequency
tuning word for a space, and the Profile 1 register is programmed
with the appropriate frequency tuning word for a mark. Then,
with the PROFILE1 and PROFILE2 pins tied to Logic 0, the
PROFILE0 pin is used to transmit the data bits. The logic state
of the PROFILE0 pin causes the appropriate mark and space
frequencies to be generated.
I/O_UPDATE PIN
By default, the I/O_UPDATE pin is an input that serves as a
strobe signal to allow synchronous update of the device operating
parameters. For example, frequency, phase, and amplitude con-
trol words for the DDS can be programmed using the serial I/O
port. However, the serial I/O port is an asynchronous interface;
consequently, programming of the device operating parameters
using the I/O port is not synchronized with the internal timing.
Using the pin, I/O_UPDATE, the user can synchronize the
application of certain programmed operating parameters with
external circuitry when new parameters are programmed into
the I/O registers. A rising edge on I/O_UPDATE initiates transfer
of the register contents to the internal workings of the device.
The transfer of programmed data from the programming
registers to the internal hardware is also accomplished by
changing the state of the profile pins.
AUTOMATIC I/O UPDATE
The AD9957 offers an option whereby the I/O update function
is asserted automatically rather than relying on an external
signal supplied by the user. This feature is enabled by setting the
internal I/O update active bit in CFR2.
When this feature is active, the I/O_UPDATE pin becomes an
output pin. It generates an active high pulse each time an inter-
nal I/O update occurs. The duration of the pulse is approximately
12 cycles of SYSCLK. This I/O update strobe can be used to
notify an external controller that the device has generated an
I/O update internally.
The repetition rate of the internal I/O update is programmed
via the serial I/O port. Two parameters control the repetition
rate. The first parameter consists of the two I/O update rate
control bits in CFR2. The second parameter is the 32-bit word
in the I/O update rate register that sets the range of an internal
counter.
The I/O update rate control bits establish a divide by 1, 2, 4, or 8
of a clock signal that runs at f
SYSCLK
. The output of the divider
clocks the aforementioned 32-bit internal counter. The repetition
rate of the I/O update is given by
B
f
f
A
SYSCLK
2
UPDATE
O
I
_
/
=
where:
A
is the value of the 2-bit word comprising the I/O update rate
control bits. The default value of A is 0.
B
is the value of the 32-bit word stored in the I/O update rate
register. The default value of B is 0xFFFF.
If B is programmed to 0x0003 or less, the I/O_UPDATE pin no
longer pulses, but assumes a static Logic 1 state.
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| AD9957BSVZ-REEL | 功能描述:IC DDS 1GSPS 14BIT IQ 100TQFP RoHS:是 類別:集成電路 (IC) >> 接口 - 直接數字合成 (DDS) 系列:- 產品變化通告:Product Discontinuance 27/Oct/2011 標準包裝:2,500 系列:- 分辨率（位）:10 b 主 fclk:25MHz 調節字寬（位）:32 b 電源電壓:2.97 V ~ 5.5 V 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:16-TSSOP（0.173"，4.40mm 寬） 供應商設備封裝:16-TSSOP 包裝:帶卷 (TR) |
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