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PRELIMINARY TECHNICAL DATA

AD9953

Continuous Bi-directional Ramp mode allows the AD9953 to offer an automatic symmetrical

sweep between two frequencies. The AD9953 is programmed for Continuous Bi-directional Ramp

mode by writing the RAM Enable bit true and the RAM Mode Control bits of each profile to be

used to logic 011(b).

Upon entering this mode (via an I/O UPDATE or changing Profile<1:0>), the RAM address

generator loads the RAM Segment Beginning Address bits of the current RSCW and the Ramp

Rate Timer loads the RAM Segment Address Ramp Rate bits. The RAM drives data from the

beginning address and the ramp rate timer begins to count down to 1. When the ramp rate timer

completes a cycle, the RAM address generator increments to the next address, the timer reloads the

ramp rate bits and continues counting down. This sequence continues until the RAM address

generator has incremented to an address equal to the RAM Segment Final Address bits of the

current RSCW. Upon reaching this terminal address, the RAM address generator will decrement

in value at the ramp rate until it reaches the RAM Segment Beginning address. Upon reaching the

beginning address, the entire sequence repeats.

The entire sequence repeats for as long as the part is programmed for this mode. The No Dwell bit

is a “don’t care” in this mode. In general, this mode is identical in control to the Bi-directional

Ramp Mode except the ramp up and down is automatic (no external control via the Profile<0>

input) and switching profiles is valid. Once in this mode, the address generator ramps from

beginning address to final address back to beginning address at the rate programmed into the ramp

rate register. This mode enables generation of an automatic saw tooth sweep characteristic.

Notes to the Continuous Bi-directional Ramp mode:

1) The user must insure that the beginning address is lower than the final address.

2) Changing profiles or issuing an I/O UPDATE automatically terminates the current sweep

and starts the next sweep.

3) Setting the RAM destination bit true such that the RAM output drives the phase-offset adder

is valid. While the above discussion describes a frequency sweep, a phase sweep operation

is also available.

Continuous Re-circulate Mode

Continuous Re-circulate mode allows the AD9953 to offer an automatic, continuous unidirectional

sweep between two frequencies. The AD9953 is programmed for Continuous Re-circulate mode

by writing the RAM Enable bit true and the RAM Mode Control bits of each profile to be used to

logic 100(b).

Upon entering this mode (via an I/O UPDATE or changing Profile<1:0>), the RAM address

generator loads the RAM Segment Beginning Address bits of the current RSCW and the Ramp

Rate Timer loads the RAM Segment Address Ramp Rate bits. The RAM drives data from the

REV. PrB 1/30/03

Page 27

Analog Devices, Inc.

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