ISL5217_05 Datasheet, PDF (14/43 Pages) Intersil Corporation – Quad Programmable Up Converter

ISL5217
0
INTERPOLATION FILTER RESPONSE
-20
-40
-60
-80
-100
-120
64 128 192 256 320 384 448
512
SAMPLE TIMES
FIGURE 13B. INTERPOLATION FILTER IMPULSE RESPONSE
L = 16; FOUT = 4096
0
-0.05
-0.1
-0.15 _{INTERPOLATION FILTER RESPONSE}
-0.2
-0.25
-0.3
-0.35
-0.4
-0.45
-0.5
-0.55
-0.6
-0.65
-0.7
8
16 24 32 40 48 56 64
SAMPLE TIMES
FIGURE 13C. INTERPOLATION FILTER IMPULSE RESPONSE
L = 16; FOUT = 4096
Carrier NCO
Following the interpolating filter section, the samples are
modulated onto a carrier signal via a complex multiply
operation. The Carrier NCO provides the quadrature local
oscillator references to the complex mixer.
The NCO has provisions for programming the frequency and
phase offset. The NCO has a 32 bit frequency control
providing sub-hertz resolution at the maximum clock rate.
The carrier NCO phase accumulator feedback can be preset
to synchronize multiple channels. The carrier NCO has a
32-bit 2’s complement programmable frequency increment
value which can range from -2³¹ to ~2³¹ for a NCO output
range of -f_CLK/2 to ~f_CLK/2. For f_CLK = 104MHz, the
frequency will range from -52MHz to +52MHz.
The maximum error is 104MHz/(2³²) = 0.0242Hz. The
carrier frequency can be calculated from the value loaded
into Control Address 0x8 and 0x9 by:
F_CARRIER = CR(31:0) × f_CLK × 2^–32
(EQ. 5)
where CR(31:0) is the 32-bit frequency control word which
can range from -2³¹ to ~2³¹ for a NCO output range of
-f_CLK/2 to ~f_CLK/2. f_CLK is the CLK frequency.
This NCO frequency range allows for spectral inversion.
Given a desired carrier frequency, the value for CR(31:0)
loaded into the part can be calculated by:
CR(31:0) = INT[F_C ⁄ f_CLK *2³² ]
(EQ. 6)
where INT[X] is the integer part of the real number X.
The vector rotation can also be controlled by the sign of the
CF value. When CF is a positive value a counterclockwise
vector rotation is produced. When CF is a negative value a
clockwise vector rotation is produced.
The carrier frequency is loaded 16 bits at a time into Control
Words 8 and 9.
0x8, bits 15:0 = CF (31:16)
0x9, bits 15:0 = CF (15:0)
The 16-bit carrier phase offset initializes the most-significant
16-bits of the phase accumulator. The least significant 16
bits of the phase accumulator are cleared. Given a desired
carrier phase offset, the value CO(31:0) can be calculated by
the following equation.
CO(31:0) = INT
(_---P_----h_----a_----s_---e_----O_-----f_---f_--s_---e_----t_--)_---°
360°
*2³² ]
(EQ. 7)
The carrier phase offset is loaded into Control Word 0x7.
Control Word 7 (15:0) = CO (31:16).
Complex Mixer
The complex mixer multiplies the sin/cos terms generated by
the carrier NCO sin/cos generator with the I and Q
interpolated sample data. The mixers can be bypassed by
programming the carrier frequency to zero. This action sets
the sin/cos terms generated by the carrier NCO to 0 and 1
respectively. The block diagram of the Carrier NCO/Complex
Mixer is shown in Figure 14.
I(20:0)
19
COS
SIN
19
+
∑_-
Re (20:0)
Q(20:0)
EN OUT
Q(20:0)
19
COS
∑⁺
SIN
19
+
Im (20:0)
I(20:0)
EN OUT
FIGURE 14. VECTOR MODULATOR/MIXER BLOCK DIAGRAM
14
FN6004.3
July 8, 2005