zl10038 ETC-unknow, zl10038 Datasheet - Page 31

• Manufacturer Part Number: zl10038
• Description: Advanced Modulation Dvb-s2 Compliant Satellite Tuner With Bypass
• Manufacturer: ETC-unknow

f
from the demodulator,
and
For low symbol rates, the energy content within the bandwidth of the filters reduces significantly so incrementing
the baseband post-filter gain helps recover the signal level for the demodulator.
N.B. During channel acquisition or re-acquisition, the filter must be set to its maximum value.
4.3.2
The -3 dB bandwidth of the filter (Hz) is given by the following expression:
Equation 1 -
Where:
f
f
K = 1.257 (constant).
BF = Decimal value of the register bits BF6:BF1, range 0 - 62.
BR = Decimal value of the bits BR4:BR0 (baseband filter reference divider ratio), range 4 - 27.
where: 575 kHz ≤
The digital nature of the control loop means that the filter bandwidth setting is quantized: the difference between the
desired filter bandwidth and the actual filter bandwidth possible due to discrete settings causes a bandwidth error.
In order to minimize this bandwidth error, the maximum filter bandwidth setting resolution is needed. From the limits
given above, the best resolution possible is 575 kHz/1.257 = 457.4 kHz. However if this resolution is used, the
maximum bandwidth with BF = 62 is only 28.82 MHz, below the maximum of 35 MHz. Therefore for filter
bandwidths greater than 28.82 MHz the resolution must be decreased. For filter bandwidths around 35 MHz the
resolution is typically reduced to 698 kHz/1.257 = 555.3 kHz.
4.3.3
4.3.3.1
The above description can be described mathematically as:
For
Equation 2 -
For
Equation 3 -
These equations can give non-integer results so rounding must be performed. The values for BR should be
rounded DOWN to the nearest integer this ensures that
programmable bandwidth will not be below the desired bandwidth due to rounding.
offs
bw
xtal
= Baseband filter –3 dB bandwidth (Hz) which should be within the range
f
f
= Crystal oscillator reference frequency (Hz).
is the total offset of the received signal due to all causes (LNB drift, synthesizer step size, etc) and is read back
f
bw
bw
bw
≤ 28.82 MHz,
> 28.82 MHz,
is the -3 dB roll-off of the filter for: 8 MHz ≤
Calculating the Filter Bandwidth
Determining the Values of BF and BR
Calculating the Value of BR
BR
BR
f
---------
BR
xtal
=
f
=
bw
≤ 2.5 MHz.
------------------- -
575kHz
f
------- -
f
xtal
bw
f
=
xtal
×
f
--------- -
BR
xtal
(
62
.
×
+
(
BF
1
)
×
+
--- -
K
1
1
)
.
×
--- -
K
1
Zarlink Semiconductor Inc.
ZL10038
f
bw
≤ 35 MHz.
31
f
-------- -
BR
xtal
will not be below 575 kHz and that the maximum
8MHz
≤
f
bw
≤
35MHz
.
Data sheet