AD9545 datasheet(119/157 Pages) AD

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Data Sheet

AD9545

Rev. A | Page 119 of 157

AUXILIARY NCOS

AUXILIARY NCO OVERVIEW

The AD9545 has two auxiliary NCOs. The NCOs generate time

stamps and/or physical output signals based on a very precise

programmable frequency specified by the user. The NCOs have

frequency tuning resolution of 2−40 Hz, or approximately 1 pHz.

Figure 93 shows a block diagram of the NCOs. The auxiliary NCOs

also provide elapsed time information to the user time stamp

processors (see the User Access to Time Stamps section).

AUXILIARY NCO FREQUENCY

The user programs the output frequency of the auxiliary NCOs

by assigning a center frequency and an offset frequency.

The center frequency assignment is via the auxiliary NCO x center

frequency bit fields (where x is 0 or 1) in Register 0x2800 to

center frequency is a 56-bit unsigned integer carrying units of

2−40 Hz. The offset frequency assignment is via the auxiliary NCO x

offset frequency bit fields (where x is 0 or 1) in Register 0x2807 to

offset frequency is a 32-bit unsigned integer carrying units of

2−24 Hz.

Figure 94 details the relationship between the center and offset

frequencies. The center frequency has an upper limit of

approximate 65 kHz, and the offset frequency has an upper limit of

approximately 256 Hz.

AUXILIARY

NCO 0

TEXT

= BIT(S) IN THE REGISTER MAP

CLOCK SOURCE

(DERIVED FROM SYSTEM CLOCK)

AUXILIARY

NCO 1

Mx PIN

SWITCH

MATRIX

PULSE

TO USER

TIME STAMP

PROCESSORS

TO DIGITAL

CROSS POINT

MUX

TIME

STAMPS

TIME

STAMPS

ELAPSED

TIME

ELAPSED

TIME

AUXILIARY NCO 0

CENTER FREQUENCY

AUXILIARY NCO 0

OFFSET FREQUENCY

AUXILIARY NCO 0

TIME CLOCK

AUXILIARY NCO 1

TIME CLOCK

AUXILIARY NCO 1

CENTER FREQUENCY

AUXILIARY NCO 1

OFFSET FREQUENCY

Figure 93. Auxiliary NCO Block Diagram

CENTER

OFFSET

2–24 Hz

2–40 Hz

...

FRACTIONAL Hz

INTEGER Hz

OUTPUT = CENTER + OFFSET

56-BIT CENTER FREQUENCY

32-BIT OFFSET FREQUENCY

DECIMAL

POINT

Figure 94. Auxiliary NCO Frequency Tuning

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