hsp50215 Intersil Corporation, hsp50215 Datasheet - Page 9

• Manufacturer Part Number: hsp50215
• Description: Digital Upconverter
• Manufacturer: Intersil Corporation

Re-Sampling NCO Application Issues
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.
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
1. Common clocking of the PUC and PDC:
2. Improving the NCO Accuracy
SYNCSEL
WR CW21
SAMPLE FREQUENCY
†
WR CW3
SYNCIN
CLOCKED AT REFLCK
ALL REGISTERS ARE
IP(1:0)
ZERO
RST
FIGURE 8. RE-SAMPLING NCO BLOCK DIAGRAM
START
EDGE
GEN
>
>
R
E
G
R
E
G
3-430
RESET
EDGE
GEN
EN
>
SHIFTER
>
2
REG
REG
REG
30
4, 3, OR 2
12
<
ACC
32
(CARRIER NCO)
EnNCO
SAMPCK
(MSB)
FINE
PHASE
COARSE
PHASE
HSP50215
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 9A. INTERPOLATION FILTER IMPULSE RESPONSE
FIGURE 9B. INTERPOLATION FILTER IMPULSE RESPONSE
FIGURE 9C. INTERPOLATION FILTER IMPULSE RESPONSE
-100
-120
-100
-120
-0.05
-0.15
-0.25
-0.35
-0.45
-0.55
-0.65
-20
-40
-60
-80
-20
-40
-60
-80
-0.1
-0.2
-0.3
-0.4
-0.5
-0.6
-0.7
0
0
0
INTERPOLATION FILTER RESPONSE
INTERPOLATION FILTER RESPONSE
512
L = 16; FOUT = 4096
64
L = 16; FOUT = 4096
L = 16; FOUT = 4096
8
1024
128
16
1536
INTERPOLATION FILTER RESPONSE
192
SAMPLE TIMES
SAMPLE TIMES
24
SAMPLE TIMES
2048
256
32
2560
320
40
384
3072
48
448
3584
56
4096
512
64