HSP50110 データシートの表示（PDF） - Intersil
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HSP50110 Datasheet PDF : 25 Pages
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HSP50110
the contents of the Carrier Frequency (CF) Register and the
Carrier Offset Frequency (COF) Register. As the
accumulator sum transitions from 0 to 232, the SIN/COS
ROM produces quadrature outputs whose phase advances
from 0o to 360o. The sum of the CF and COF Registers
represent a phase increment which determines the
frequency of the quadrature outputs. Large phase
increments take fewer clocks to transition through the sine
wave cycle which results in a higher frequency NCO output.
The NCO frequency is set by loading the CF and COF
Registers. The contents of these registers set the NCO
frequency as given by the following,
FC = FS x (CF + COF)/232,
(EQ. 5)
where fS is the sample rate set by the Input Controller, CF is
the 32-bit two’s complement value loaded into the Carrier
Frequency Register, and COF is the 32-bit two’s
complement value loaded into the Carrier Offset Frequency
Register. This can be rewritten to have the programmed CF
and COF value on the left:
(CF + COF) = INT[(FC/FS)232]HEX
(EQ. 5A)
As an example, if the CF Register is loaded with a value of
3000 0000 (Hex), the COF Register is loaded with a value of
1000 0000 (Hex), and the input sample rate is 40 MSPS, an
the NCO would produce quadrature terms with a frequency
of 10MHz. When the sum of CF and COF is a negative
value, the cos/sin vector generated by the NCO rotates
clockwise which downconverts the upper sideband; when
the sum is positive, the cos/sin vector rotates
counterclockwise which upconverts the lower sideband.
Note: the input sample rate FS is determined by the rate
at which ENI is asserted low (see Input Controller
Section). If ENI is tied low, the input sample rate is equal
to the CLK rate.
The Carrier Frequency Register is loaded via the
Microprocessor Interface and the Carrier Offset Frequency is
loaded serially using the COF and COFSYNC inputs. The
procedure for loading these registers is discussed in the
Microprocessor Interface Section and the Serial Input
Section.
The phase of the NCO’s quadrature outputs can be adjusted
by adding an offset value to the output of the phase
accumulator as shown in Figure 2. The offset value can be
loaded into the Phase Offset (PO) Register or input via the
PH0-1 inputs. If the PO Register is used, the phase can be
adjusted from -π to π with a resolution of ~1.4o. The phase
offset is given by the following equation,
φ = π x (PO/128),
(EQ. 6)
where PO is the 8-bit two’s complement value loaded into the
Phase Offset Register (see Phase Offset Register in Table 12).
As an example, a value of 32, (20HEX), loaded into the Phase
Offset Register would produce a phase offset of 45o.
An alternative method for controlling the NCO Phase uses
the PH0-1 inputs to shift the phase of NCO’s output by 0o,
90o, 180o, or 270o. The PH0-1 inputs are mapped to phase
shifts as shown in Table 1. The phase may be updated every
clock supporting the π/2 phase shifts required for modulation
or despreading of CDMA signals.
The output of the complex multiplier is scaled by 2-36. See
“Setting DQT Gains” below.
TABLE 1. PH0-1 INPUT PHASE MAPPING
PH1-0
00
01
10
11
PHASE SHIFT
0o
90o
270o
180o
AGC
The level of the Mixer output is gain adjusted by an AGC
closed around the Low Pass Filtering. The AGC provides the
coarse gain correction necessary to help maintain the output
of the HSP50110 at a signal level which maintains an
acceptable dynamic range. The AGC consists of a Level
Detector which generates an error signal, a Loop Gain
multiplier which amplifies the error, and a Loop Filter which
integrates the error to produce gain correction (see
Figure 4).
The Level Detector generates an error signal by comparing
the magnitude of the DQT output against a user
programmable threshold (see AGC Control Register in Table
8). In the normal mode of operation, the Level Detector
outputs a -1 for magnitudes above the threshold and +1 for
those below the threshold. The ±1 outputs are then multiplied
by a programmable loop gain to generate the error signal
integrated by the Loop Filter. The Level Detector uses the
magnitude estimation algorithm described in the Input Level
Detector Section. The sense of the Level Detector Output may
be changed via the Chip Configuration Register, bit 0 (see
Table 11).
The Loop Filter consists of a multiplier, an accumulator and a
programmable limiter. The multiplier computes the product of
the output of the Level Detector and the Programmable Loop
Gain. The accumulator integrates this product to produce the
AGC gain, and the limiter keeps the gain between preset
limits (see AGC Control Register, Table 8). The output of the
AGC Loop Filter Accumulator can be read via the
Microprocessor Interface to estimate signal strength (see
Microprocessor Interface Section).
The Loop Filter Accumulator uses a pseudo floating point
format to provide up to ~48dB of gain correction. The format
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