AD6622AS Analog Devices Inc, AD6622AS Datasheet - Page 25

• Manufacturer Part Number: AD6622AS
• Manufacturer: Analog Devices Inc

Specifications of AD6622AS

• Lead Free Status / RoHS Status: Not Compliant

Bit 5 Reserved. Must be set low.
Bits 7:6 set the RCF Coarse Scale as shown below.
(0xn0E) Reserved
(0xn0F) Reserved
(0xn10) Reserved (Must Be Written to 0)
(0xn11) Reserved (Must Be written to 0)
(0xn12–0xn1F) Reserved
(0xn20–0xn3F) Data Memory
This group of registers contain the RCF Filter Data. See the RCF
section of the data sheet for additional detail.
(0xn40–0xn7F) Reserved
(0xn80–0xnFF) Coefficient Memory
This group of registers contain the RCF Filter Coefficients. See
the RCF section of the data sheet for additional detail.
WRITE PSEUDOCODE
Void Write_Micro(ext_address, int data);
Main()
{
/ This code shows the programming of the NCO frequency
register using the Write_Micro function defined above. The
variable address is the External Address A[2:0] and data is the
value to be placed in the external interface register.
Internal Address = 0x102, channel 1
/ Holding registers for NCO byte wide access data /
int d3, d2, d1, d0;
/ NCO frequency word (32 bits wide) /
NCO_FREQ=0x1BEFEFFF;
/ write Chan /
Write_Micro(7, 0x01);
/ write Addr /
Write_Micro(6,0x02);
/ write Byte 3 /
d3=(NCO_FREQ & 0xFF000000)>>24;
Write_Micro(3,d3);
/ write Byte 2 /
d2=(NCO_FREQ & 0xFF0000)>>16;
Write_Micro(2,d2);
/ write Byte 1 /
d1=(NCO_FREQ & 0xFF00)>>8;
Write_Micro(1,d1);
/ write Byte 0, Byte 0 is written last and causes an internal write
to occur /
d0=NCO_FREQ & 0xFF;
Write_Micro(0,d0);
}
/
Bit 7
0
0
1
1
Table XVI. RCF Scaling
Bit 6
0
1
0
1
RCF Coarse Scale
0 dB
–6 dB
–12 dB
–18 dB
READ PSEUDOCODE
Void Read_Micro(ext_address);
Main()
{
/* This code shows the reading of the NCO frequency register
using the Read_Micro function defined above. The variable
address is the External Address A[2:0]
Internal Address = 0x102, channel 1
/ Holding registers for NCO byte wide access data /
int d3, d2, d1, d0;
/ NCO frequency word (32 bits wide) /
/ write Chan /
Write_Micro(7, 0x01);
/ write Addr /
Write_Micro(6,0x02);
/ read Byte 0, all data is moved from the Internal Registers to
the interface registers on this access, thus Byte 0 must be accessed
first for the other Bytes to be valid /
d0=Read_Micro(0) & 0xFF;
/ read Byte 1 /
d1=Read_Micro(1) & 0xFF;
/ read Byte 2 /
d2=Read_Micro(2) & 0xFF;
/ read Byte 0 /
d3=Read_Micro(3) & 0xFF;
}
APPLICATIONS
The AD6622 provides considerable flexibility for the control of
the synchronization, relative phasing, and scaling of the individual
channel inputs. Implementation of a multichannel transmitter
invariably begins with an analysis of the output spectrum that
must be generated.
DIGITAL-TO-ANALOG CONVERTER (DAC) SELECTION
The selection of a high-performance DAC depends on a number
of factors. The dynamic range of the DAC must be considered
from a noise and spectral purity perspective. The 14-bit AD9754
and AD9772 are the best choices for overall bandwidth, noise,
and spectral purity.
In order to minimize the complexity of the analog interpolation
filter which must follow the DAC, the sample rate of the master
clock is generally set to at least three times the maximum analog
frequency of interest.
In the case where a 15 MHz band of interest is to be up-converted
to RF, the lowest frequency might be 5 MHz and the upper
band edge at 20 MHz (offset from dc to afford the best image
reject filter after the first digital IF). The minimum sample rate
would be set to 75 MSPS.
Consideration must also be given to data rate of the incoming
data stream, interpolation factors, and the clock rate of the DSP.
/
AD6622