AD6622SSLASHPCB datasheet(25/28 Pages) AD

25 / 28 page

AD6622

–25–

REV. 0

Bit 5 Reserved. Must be set low.

Bits 7:6 set the RCF Coarse Scale as shown below.

Table XVI. RCF Scaling

Bit 7

Bit 6

RCF Coarse Scale

0 dB

–6 dB

–12 dB

–18 dB

(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

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);

}

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.

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