AD6674 datasheet(48/97 Pages) AD

48 / 97 page

Data Sheet

AD6674

Rev. C | Page 47 of 96

FREQUENCY TRANSLATION

GENERAL DESCRIPTION

Frequency translation is accomplished by using a 12-bit

complex NCO with a digital quadrature mixer. This stage

translates either a real or complex input signal from an IF to a

baseband complex digital output (carrier frequency = 0 Hz).

The frequency translation stage of each DDC can be controlled

individually and supports four different IF modes using Bits[5:4]

of the DDC control registers (Register 0x310, Register 0x330,



Variable IF mode



0 Hz IF or zero IF (ZIF) mode



fS/4 Hz IF mode



Test mode

Variable IF Mode

NCO and mixers are enabled. NCO output frequency can be

used to digitally tune the IF frequency.

0 Hz IF (ZIF) Mode

The mixers are bypassed, and the NCO is disabled.

fS/4 Hz IF Mode

The mixers and the NCO are enabled in special downmixing by

fS/4 mode to save power.

Test Mode

Input samples are forced to 0.999 to positive full scale. The

NCO is enabled. This test mode allows the NCOs to directly

drive the decimation filters.

Figure 104 and Figure 105 show examples of the frequency

translation stage for both real and complex inputs.

BANDWIDTH OF

INTEREST

BANDWIDTH OF

INTEREST IMAGE

NCO FREQUENCY TUNING WORD (FTW) SELECTION

12-BIT NCO FTW = MIXING FREQUENCY/ADC SAMPLE RATE × 4096

ADC + DIGITAL MIXER + NCO

REAL INPUT—SAMPLED AT

–

fS/2

–

fS/3

–

fS/4

–

fS/8

fS/16

fS/8

fS/4

fS/3

fS/2

–

fS/16

–

fS/32

–

fS/32

–

fS/32

cos(wt)

0°

90°

ADC

SAMPLING

REAL

–sin(wt)

12-BIT

NCO

POSITIVE FTW VALUES

NEGATIVE FTW VALUES

COMPLEX

–6dB LOSS DUE TO

NCO + MIXER

12-BIT NCO FTW =

ROUND ((

fS/3)/fS × 4096) = +1365 (0x555)

12-BIT NCO FTW =

ROUND ((

fS/3)/fS × 4096) = –1365 (0xAAB)

Figure 104. DDC NCO Frequency Tuning Word Selection—Real Inputs

AD6674 Datasheet(PDF) 48 Page - Analog Devices

AD6674 Datasheet(HTML) 48 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97

Datasheet Download

Link URL