ISL5416KI Intersil, ISL5416KI Datasheet - Page 19

• Manufacturer Part Number: ISL5416KI
• Description: Up/Down Conv Mixer 1.8V 256-Pin BGA
• Manufacturer: Intersil

Specifications of ISL5416KI

• Package: 256BGA
• Operating Supply Voltage: 1.8 V

Interpolation Half Band Filter / Re-sampling Filter
A rate change section follows the AGC. This section is used
to resample the signal from FIR2 to increase the sample rate
for finer time resolution and/or to resample the data to
another sample spacing. This section consists of an
interpolation half-band filter, an interpolating resampling
filter, a decimation counter/sampler, a FIFO, a set of NCOs,
and a “leap” counter. This processing stage allows the
filtering in FIR2 to be done at the lowest sample rate that
meets the Nyquist criteria and the data then resampled to
the desired final sample rate. The output/input sample rate
ratio can be almost any value from 0.125 to >4096. A block
diagram is provided below in Figure 8.
The re-sampling filter (HOIF) can accept inputs at any rate
up to its maximum output rate of one half the clock rate.
Preceding the resampler is an interpolation halfband filter.
This filter can be used to provide a fixed interpolation by 2
when the resampler is bypassed or, when used with the
resampler, to increase the image-free dynamic range of the
output. The IHBF can output at up to the clock rate if the
resampling filter is bypassed and up to one half the clock
rate if the resampling filter is enabled. Frequency response
plots are provided below for the half-band and resampling
filters. An example frequency response for a FIR2 response
together with the half-band and resampling filters is also
provided.
The resampling process produces images of the signal at
multiples of the input sample rate. Large interfering signals
must be removed from the spectrum with the CIC, FIR1, and
FIR2 filters or the images created from them in the
resampling process may cause problems. The level of the
images created by resampling process has a fixed dBc level
for a given set of filters and sampling ratio. As the signal level
in the channel increases and decrease, the images levels
will increase and decrease by the same amount. As the ratio
of the FIR2 output sample rate to the band edge increases,
the level, in dBc, of the images decreases.
19
ISL5416
-100
FIGURE 7C. INDIVIDUAL AND COMPOSITE RESPONSES (FIR2
-20
-40
-60
-80
-10
-20
-30
-40
-50
-60
-70
-80
10
-10
-20
-30
-40
-50
-60
-70
-80
10
0
FIGURE 7B. IHBF (INTERPOLATE BY 2) AND RE-
0
0
0
0
FIGURE 7A. INTERPOLATION HALF BAND RESPONSE
OUTPUT AT 7.68 MHz WITH IHBF, INTERPOLATE BY 2)
0
0.5
SAMPLER (INTERPOLATE BY 2)
5
1
5
1.5
10
2
10
2. 5
x 10
x 10
x 10
15
6
3
15
7
6