HSP50215VC datasheet(9/21 Pages) INTERSIL

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Re-Sampling NCO Application Issues

1. Common clocking of the PUC and PDC:

Note that at a board level, the HSP50214 (PDC) and

HSP50215 (DUC) sample rate NCO’s typically utilize

different clocks. The DUC circuitry is clocked at the master

clock, REFCLK, rate. The PDC output circuitry runs off the

decimated sample rate. If a common sample clock is used

for both parts, then synchronization can be achieved by

scaling and/or truncating the PDC frequency control word to

match the PUC frequency control word. Powers of 2 are

handled by simply truncating the PDC frequency control

word to match the bit width of the DUC frequency control

word. If the PDC decimation factor is not power of 2, then

errors will accumulate.

2. Improving the NCO Accuracy

The Re-Sampler NCO frequency can be adjusted to

maintain phase and frequency lock to a reference clock, if

more accuracy is required.

Interpolation Filter

The Interpolation ﬁlter provides sampling rate conversion

from the shaping ﬁlter output rate to the ﬁnal output sample

rate. The nulls in the interpolation ﬁlter frequency response

align with the interpolation images of the shaping ﬁlter. The

impulse response of the Interpolation ﬁlter is shown in

Figures 9A through 9C for an interpolate by 16 ﬁlter (the

interpolation ratio, L, is equal to 16). The Interpolation ﬁlter

has a pipeline delay of 3 coarse input samples plus 3

REFCLK cycles.

FIGURE 8. RE-SAMPLING NCO BLOCK DIAGRAM

SYNCIN

WR CW3

SAMPLE FREQUENCY

ZERO

SHIFTER

IP(1:0)

FINE

PHASE

COARSE

PHASE

SAMPCK

(MSB)

SYNCSEL

† ALL REGISTERS ARE

CLOCKED AT REFLCK

4, 3, OR 2

∑

REG

EnNCO

(CARRIER NCO)

ACC

START

GEN

EDGE

RESET

GEN

EDGE

WR CW21

RST

FIGURE 9A. INTERPOLATION FILTER IMPULSE RESPONSE

L = 16; FOUT = 4096

FIGURE 9B. INTERPOLATION FILTER IMPULSE RESPONSE

L = 16; FOUT = 4096

FIGURE 9C. INTERPOLATION FILTER IMPULSE RESPONSE

L = 16; FOUT = 4096

-20

-40

-60

-80

-100

-120

512

1024

1536

2048

2560

3072

3584

4096

SAMPLE TIMES

INTERPOLATION FILTER RESPONSE

-20

-40

-60

-80

-100

-120

128

192

256

SAMPLE TIMES

320

384

448

512

INTERPOLATION FILTER RESPONSE

-0.05

-0.1

-0.15

-0.2

-0.25

-0.3

-0.35

-0.4

-0.45

-0.5

-0.55

-0.6

-0.65

-0.7

24324048

SAMPLE TIMES

INTERPOLATION FILTER RESPONSE

HSP50215

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