AD9083BBCZ datasheet(38/93 Pages) AD

38 / 93 page

AD9083

Data Sheet

Rev. 0 | Page 38 of 93

Decimate by J Filters

After the frequency translation stage, there are multiple

decimation filter stages that reduce the output data rate. After

the carrier of interest is tuned down to dc (carrier frequency =

0 Hz), these filters efficiently lower the sample rate, while

providing sufficient alias rejection from unwanted adjacent

carriers around the bandwidth of interest.

When the decimate by J block is supplied with direct data from

the ADC, there is no mixing option. Only decimation occurs.

The valid J decimation options are determined by the path

before the decimate by J block. Table 19 lists the available J

decimation options determined by the input data path.

The decimate by J block supports decimation ratios of 1, 4, 8, 10,

12, 16, 20, 24, 30, 40, and 60, as shown in Table 19.

Decimation rates of 1, 4, 10, and 30 are valid only when CIC is

not bypassed (for example, DECI_ADC_DATA is equal to 0).

Figure 81 shows the detailed block diagram of the Decimate by

J filters.

Table 12 describes the filter characteristics of the different FIR filter

blocks.

Table 21 shows the different filter configurations selectable by

including different filters. In all cases, the decimate by J filtering

stage provides 81.4% of the available output bandwidth,

<±0.005 dB of pass-band ripple, and >100 dB of stop band alias

rejection. Table 22 shows the coefficients for the various finite

impulse response (FIR) filters used in the AD9083.

FROM MIXER/CIC

DIRECT FROM ADC

HB1

HB2

HB4

PB2

HB3

TB3

Figure 81. Decimate by J Filters Block Diagram

Table 19. J Decimation Rate

CIC Filter and NCO0/Mixer Bypassed

(DECI_ADC_DATA = 1 and

NO_DDC_MODE = 1)

CIC Filter Enabled and NCO0/Mixer

Bypassed (DECI_ADC_DATA = 0 and

NO_DDC_MODE = 1)

CIC Filter and NCO0/Mixer Enabled

(DECI_ADC_DATA = 0 and

NO_DDC_MODE = 0)

Invalid

1 (bypass mode)

Invalid

Table 20. Decimation Filter Characteristics

Filter Name

Decimation Ratio

Pass Band

(rad/sec)

Stop Band (rad/sec)

Pass-Band Ripple (dB)

Stop Band Rejection (dB)

HB4

0.1 × π/2

π/2 × 1.9

<±0.001

>100

HB3

0.2 × π/2

π/2 × 1.8

<±0.001

>100

HB2

0.4 × π/2

π/2 × 1.6

<±0.001

>100

HB1

0.8 × π/2

π/2 × 1.2

<±0.001

>100

TB3

0.3 × π/3

π/3 × 1.8

<±0.001

>100

PB2

0.4 × π/5

π/5 × 1.6

<±0.001

>100

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