HSP45116AVC-52 Intersil, HSP45116AVC-52 Datasheet - Page 10

• Manufacturer Part Number: HSP45116AVC-52
• Manufacturer: Intersil

Specifications of HSP45116AVC-52

• Mounting Style: Surface Mount
• Screening Level: Commercial
• Lead Free Status / RoHS Status: Not Compliant

The Phase Accumulator consists of registers and adders
that compute the value of the current phase at every clock. It
has three inputs: Center Frequency, which corresponds to
the carrier frequency of a signal; Offset Frequency, which is
the deviation from the Center Frequency; and Phase, which
is a 16-bit number that is added to the current phase for PSK
modulation schemes. These three values are used by the
Phase Accumulator and Phase Adder to form the phase of
the internally generated sine and cosine.
The sum of the values in Center and Offset Frequency
Registers corresponds to the desired phase increment
(modulo 2
loading both registers with zero will cause the Phase
Accumulator to add zero to its current output; the output of
the PFCS will remain at its current value; i.e., the output of
the NCOM will be a DC signal. If a hexadecimal 00000001 is
loaded into the Center Frequency Control Register, the
output of the PFCS will increment by one after every clock.
This will step through every location in the Sine/Cosine
Generator, so that the output will be the lowest frequency
above DC that can be generated by the NCOM, i.e., the
clock frequency divided by 2
Frequency Control Register is hex 80000000, the PFCS will
step through the Generator with half of the maximum step
size, so that frequency of the output waveform will be half of
the sample rate.
The operation of the Offset Frequency Control Register is
identical to that of the Center Frequency Control Register;
having two separate registers allows the user to generate an
FM signal by loading the carrier frequency in the Center
Frequency Control Register and updating the Offset
Frequency Control Register with the value of the frequency
offset - the difference between the carrier frequency and the
frequency of the output signal. A logic low on CLROFR
disables the output of the Offset Frequency Register without
clearing the contents of the register.
Initializing the Phase Accumulator Register is done by putting
a low on the LOAD line. This zeroes the feedback path to the
accumulator, so that the register is loaded with the current
value of the phase increment summer on the next clock.
The final phase value going to the Generator can be
adjusted using MODPI/2PI to force the range of the phase to
be 0
2π is the mode used for modulation, demodulation, direct
digital synthesis, etc. Modulo π is used to calculate FFTs.
This is explained in greater detail in the Applications Section.
o
MOD1
to 180
0
0
1
1
32
) from one clock to the next. For example,
o
(modulo π) or 0
TABLE 2. MOD0-1 DECODE
MOD0
0
1
0
1
32
10
o
. If the input to the Center
to 360
PHASE SHIFT (DEGREES)
o
(modulo 2π). Modulo
270
180
90
0
HSP45116A
The Phase Register adds an offset to the output of the
Phase Accumulator. Since the Phase Register is only 16
bits, it is added to the top 16 bits of the Phase Accumulator.
The Time Accumulator consists of a register which is
incremented on every clock. The amount by which it
increments is loaded into the Input Registers and is latched
into the Time Accumulator Register on rising edges of CLK
while ENTIREG is low. The output of the Time Accumulator
is the accumulator carry out, TICO. TICO can be used as a
timer to enable the periodic sampling of the output of the
NCOM. The number programmed into this register equals
2
its phase is initialized by zeroing the feedback path of the
accumulator with RBYTILD.
Sine/Cosine Section
The Sine/Cosine Section (Figure 2) converts the output of
the PFCS into the appropriate values for the sine and
cosine. It takes the most significant 20 bits of the PFCS
output and passes them through a look up table to form the
16-bit sine and cosine inputs to the CMAC.
The 20-bit word maps into 2π radians so that the angular
resolution is 2π/2
0 radians and an address of hex FFFFF corresponds to
2π- (2π/2
are 2’s complement sine and cosine values. The sine and
cosine outputs range from hexadecimal 8001, which
represents negative full scale to 7FFF, which represents
positive full scale. Note that the normal range for two’s
complement numbers is 8000 to 7FFF; the output range of
the SIN/COS generator is scaled by one so that it is
symmetric about 0.
The sine and cosine values are computed to reduce the
amount of ROM needed. The magnitude of the error in the
computed value of the complex vector is less than -90.2dB.
The error in the sine or cosine alone is approximately
2dB better.
If RBYTILD is low, the output of the PFCS goes directly to
the inputs of the CMAC. If the real and imaginary inputs of
the CMAC are programmed to hex 7FFF and 0 respectively,
then the output of the PFCS will appear on output bits 0
R.RBYTILD
32
x CLK period/desired time interval. TICO is disabled and
32
CLK
20
20
) radians. The outputs of the Generator Section
FIGURE 2. SINE/COSINE SECTION
SINE/COSINE
GENERATOR
20
. An address of zero corresponds to
32
16
16
REG
CLK
16
16
MUX
16
16
May 7, 2007
FN4156.4
SIN
COS