AD9864 Analog Devices, AD9864 Datasheet - Page 22

• Manufacturer Part Number: AD9864
• Description: IF Digitizing Subsystem
• Manufacturer: Analog Devices

Specifications of AD9864

• Resolution (bits): 24bit
• # Chan: 1
• Sample Rate: 18MSPS
• Interface: Ser,SPI
• Analog Input Type: Diff-Uni,SE-Uni
• Adc Architecture: Sigma-Delta
• Pkg Type: CSP

AD9864
Table 10 lists the typical output rise/fall times as a function of DS
for a 10 pF load. Rise/fall times for other capacitor loads can be
determined by multiplying the typical values presented by a scal-
ing factor equal to the desired capacitive load divided by 10 pF.
Table 10. Typical Rise/Fall Times (±25%) with a 10 pF
Capacitive Load for Each DS Setting
DS
0
1
2
3
4
5
6
7
SYNCRONIZATION USING SYNCB
Many applications require the ability to synchronize one or
more AD9864s in a way that causes the output data to be pre-
cisely aligned to an external asynchronous signal. For example,
receiver applications employing diversity often require syn-
chronization of multiple AD9864s’ digital outputs. Satellite
communication applications using TDMA methods may
require synchronization between payload bursts to compensate
for reference frequency drift and Doppler effects.
SYNCB can be used for this purpose. It is an active-low signal
that clears the clock counters in both the decimation filter and
the SSI port. The counters in the clock synthesizers are not reset
because it is presumed that the CLK signals of multiple chips
would be connected. SYNCB also resets the modulator, result-
ing in a large-scale impulse that must propagate through the
AD9864’s digital filter and SSI data formatting circuitry before
recovering valid output data. As a result, data samples unaf-
fected by this SYNCB induced impulse can be recovered 12
output data samples after SYNCB goes high (independent of
the decimation factor).
14
13
12
11
10
8
9
7
1
(VDDx = 3.0 V, F
Figure 35. NF vs. SSI Output Drive Strength
2
SSI OUTPUT DRIVE STRENGTH SETTING
Typ (ns)
13.5
7.2
50
3.7
3.2
2.8
2.3
2.0
3
CLK
24-BIT I/O DATA
= 18 MSPS, BW = 75 kHz)
4
16-BIT I/O DATA
5
w/DVGA ENABLED
16-BIT I/O DATA
6
7
Rev. 0 | Page 22 of 44
Figure 36 shows the timing relationship between SYNCB and
the SSI port’s CLKOUT and FS signals. SYNCB is an asynchro-
nous active-low signal that must remain low for at least half an
input clock period, i.e., 1/(2 × f
while FS remains low upon SYNCB going low. CLKOUT will
become active within one to two output clock periods upon
SYNCB returning high. FS will reappear several output cycles
later, depending on the digital filter’s decimation factor and the
SSIORD setting. Note that for any decimation factor and
SSIORD setting, this delay is fixed and repeatable. To verify
proper synchronization, the FS signals of the multiple AD9864
devices should be monitored.
CLKOUT
INTERFACING TO DSPs
The AD9864 connects directly to an Analog Devices program-
mable digital signal processor (DSP). Figure 37 illustrates an
example with the Blackfin® series of ADSP-2153x processors.
The Blackfin DSP series of 16-bit products is optimized for
telecommunications applications with its dynamic power man-
agement feature, making it well suited for portable radio prod-
ucts. The code compatible family members share the funda-
mental core attributes of high performance, low power con-
sumption, and the ease-of-use advantages of a microcontroller
instruction set.
As shown in Figure 37, AD9864’s synchronous serial interface
(SSI) links the receive data stream to the DSP’s serial port
(SPORT). For AD9864 setup and register programming, the
device connects directly to ADSP-2153x’s SPI port. Dedicated
select lines (SEL) allow the ADSP-2153x to program and read
back registers of multiple devices using only one SPI port. The
DSP driver code pertaining to this interface is available on the
AD9864 Web page.
SYNCB
FS
Figure 37. Example of AD9864 and ADSP-2153x Interface
SPI
SSI
AD9864
DOUTBM
DOUTAD
CLKOUT
Figure 36. SYNCB Timing
PC
PE
PD
FS
CLK
). CLKOUT remains high
SCK
SEL
MOSI
ISO
RSCLK
RFS
R
ADSP-2153x
SPI-PORT
SERIAL
PORT