PDSP16510A Datasheet, PDF (16/23 Pages) Mitel Networks Corporation – Stand Alone FFT Processor

PDSP16510A
firstly through the Auxiliary inputs and then through the Real
inputs.
BIT 10:9
These bits define a single device system, or one of three
multiple device possibilities. The choice between the first and
second multiple device mode is dependent on the transform
size and the sampling rate needed. The third mode should
only be used when overlapped multiple transforms with less
than 1024 points are to be performed simultaneously. It
changes the LFLG logic and allows sampling rates up to the
system clock rate to be achieved with multiple output proces-
sors.
BIT 11
BITS Dec'
2:0 000
001
010
011
100
101
110
111
3
0
1
OPTION
16 x 16 COMPLEX
4 x 64 COMPLEX
256 COMPLEX
1024 COMPLEX
8 X 64 REAL
2 X 256 REAL
2 X 1024 REAL
NOT USED
SHIFT 3 PLACES AFTER PASS1
ALWAYS SHIFT 2 PLACES
5:4 00
01
10
11
RECTANGULAR
HAMMING WINDOW
BLACKMAN-HARRIS
INVERSE TRANSFORM
8:6 000
001
010
011
100
101
110
111
10:9 00
01
10
11
11
00
01
NO OVERLAP
50% OVERLAP
50% OVERLAP AND DIS ÷ 2
75% OVERLAP
75% OVERLAP AND DIS ÷ 4
DUAL SOURCE, NO OVERLAP
DUAL SOURCE, 50% OVERLAP
DUAL SOURCE, 75% OVERLAP
SINGLE DEVICE
N DEVICES, CONCURRENT I/O
N DEVICES, LOAD-TRANS-DUMP
SPECIAL MULTIPLE TRANSFORM
DAV NOT DELAYED
24 CLK DAV DELAY
12
0
1
INEN EDGE ACTIVATED
INEN IS SIMPLE ENABLE
14:13 00
01
10
11
O/P FIRST QUARTER
O/P FIRST HALF
O/P LAST HALF
O/P ALL RESULTS
15
16
0
NORMAL DAV
1
KEEP DAV ACTIVE TILL INEN
Table 6. Mode Control Bit Allocations
When this bit is set the PDSP16510 will not generate DAV
until 24 DOS clocks after data was actually valid. In this case
the output tri-state drivers will be enabled at the correct time,
even though the DAV signal was not externally valid. Host
controlled dumping should not be used.
BIT 12
When this bit is set in the single device mode, the INEN
input is a simple load enable signal. When it is reset an INEN
edge is needed at the end of a load sequence before a new
one can commence.
When it is reset in a multiple device mode it has no
action, but when it is set it will cause the DEF high going edge
to also initiate a load operation.
BIT 14:13
These bits allow four dump size options to be provided.
Individual frequency bins are not accessible.
BIT 15
Under normal circumstances DAV would be expected to
go invalid when a transform has been dumped. In some
applications, however, it may be necessary to read the outputs
more than once. When this bit is set, DAV will remain valid until
the next INEN input, and will indicate that the transformed data
still remains in the internal buffer. As soon as the next INEN is
received the transformed data will be overwritten. Whilst DAV
remains active the output tri-states will be enabled.
WINDOW OPERATORS
Since only a finite segment of a signal can be observed and
processed at any one time, it is impossible to obtain pure
spectral lines. Discontinuities are introduced at the bounda-
ries of the observation interval which lead to spectral leakage.
Windows are weighting functions applied to the data in order
to reduce these discontinuities at the boundaries.
In the time domain the signal has to be observed through
a finite window as a matter of accord. This is in fact equivalent
to multiplying the signal with a set of uniform weights i.e. a
rectangular window operator. In the frequency domain the
spectrum of the data will be the spectrum of this weighting
function shifted to the sinusoidal frequencies of the compo-
nents in the data.
The rectangular window has a Fourier Transform which is
a SINC(X) function. This has sidelobes which are only 13dB
down from the main lobe. This severely limits the dynamic
range of the system since a second sinusoid in close proximity
would have its main lobe swamped by this side lobe. This
would occur if its amplitude was a mere 13dB down from the
first sinusoid.
Window operators are thus mathematically constructed
to cancel these sidelobes as far as possible. Unfortunately this
is normally done at the expense of making the main lobe
spread over more frequency bins. This reduces the ability of
the system to resolve two frequencies, and can only be
overcome by using more data samples. This may not always
be possible because of other system constraints.
A common rule of thumb defines the resolution of an FFT
system as half the full width of the mainlobe. The width of the
mainlobe for a rectangular window is two frequency bins; for
the Hamming window it is four bins; for the Blackman-Harris