ADC34RF52 datasheet(39/105 Pages) TI

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6.3.5.4 Numerically Controlled Oscillator (NCO)

Each digital down-converter (DDC) uses a 48-bit numerically controlled oscillator (NCO) to fine tune the

frequency placement prior to the digital filtering. Different NCO frequencies for each DDC are programmed using

SPI register writes and the desired NCO frequency can be selected using SPI or the GPIO pins. When using the

GPIO pins for NCO frequency control, frequency hopping can be achieved in less than 1 µs. The digital NCO is

designed to have a SFDR of at least 100 dB. The number of available, programmable NCO frequencies depends

on the number of DDC bands used as shown in Table 6-19.

ADC

NCO

GPIO

or SPI

Freq f1

Freq fX

DDC

Figure 6-38. Phase Coherent NCO Block Diagram

Table 6-19. Available No. of Frequencies per NCO

depending on No. of DDCs used

No. of DDCs used

No. of Frequencies per NCO

There are two different NCO operating modes available. Phase continuous and infinite phase coherent.

1. Phase Continuous NCO: During a NCO frequency change, the NCO phase gradually adjusts to the new

frequency as shown in Figure 6-39. The dashed line shows the phase of original f1 frequency.

2. Infinite Phase Coherent NCO: With a phase coherent NCO, all frequencies are synchronized to a single

event using SYSREF. This enables an infinite amount of frequency hops without the need to reset the NCO

as phase coherency is maintained between frequency hops. This is illustrated in Figure 6-39 (right). When

returning to the original frequency f1, the NCO phase appears as if the NCO had never changed frequencies.

Figure 6-39. Phase Continuous (left) and Infinite Phase Coherent (right) NCO Frequency Switching

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ADC34RF55

SBAS988 – NOVEMBER 2023

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ADC34RF52 Datasheet(PDF) 39 Page - Texas Instruments