AD9953_15 datasheet(23/32 Pages) AD

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AD9953

Rev. A | Page 23 of 32

nt of 1

he first method of loading is by changing the OSK input pin.

hen the OSK input pin changes state, the ASFR value is

aded into the ramp rate timer, which then proceeds to count

own as normal.

he second method in which the sweep ramp rate timer can be

aded before reaching a count of 1 is if the load OSK timer bit

FR1<26>) is set and an I/O UPDATE is issued.

he third method in which the sweep ramp rate timer can be

oaded before reaching a count of 1 is when going from the

active auto shaped on-off keying mode to the active auto

aped on-off keying mode; that is, when the sweep enable bit is

eing set.

OSK PIN

SYN

TO D

OSK Ramp Rate Timer

The OSK ramp rate timer is a loadable down counter, which

generates the clock signal to the 14-bit counter that generates

the internal scale factor. The ramp rate timer is loaded with the

value of the ASFR every time the counter reaches 1 (decimal).

This load and countdown operation continues for as long as the

timer is enabled, unless the timer is forced to load before

reaching a count of 1.

If the load OSK timer bit (CFR1<26>) is set, the ramp rate

timer is loaded upon an I/O UPDATE or upon reaching a value

a cou

of 1. The ramp timer can be loaded before reaching

by three methods.

DDS CORE

OSK ENAB

CFR<25

AMPLITUDE SCALE

FACTOR REGISTER

(ASF)

LOAD OSK TIMER

CFR1<26>

C_CLK

AUTO DESK

ENABLE

CFR1<24>

RAMP RATE TIMER

CLOCK

AUTO SCALE

CTOR GENERATO

HOLD

EC ENABLE

INC/D

OUT

COS(X)

AMPLITUDE RAMP

RATE REGISTER

(ASF)

UP/DN

DATA

LOAD

f Shaped Key

Figure 20. On-Of

ing Block Diagram

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