AD6635BB Analog Devices Inc, AD6635BB Datasheet - Page 31

• Manufacturer Part Number: AD6635BB
• Description: IC,RF/Baseband Circuit,CMOS,BGA,324PIN,PLASTIC
• Manufacturer: Analog Devices Inc
• Series: AD6635r

Specifications of AD6635BB

• Rohs Status: RoHS non-compliant
• Rf Type: Cellular, CDMA2000, EDGE, GPRS, GSM
• Number Of Mixers: 1
• Current - Supply: 880mA
• Voltage - Supply: 3 V ~ 3.6 V
• Package / Case: 324-BGA
• Frequency: -
• Gain: -
• Noise Figure: -
• Secondary Attributes: -

Although this data must be written in pages, the internal core
handles filters that exceed the length of 128 taps. Therefore, the
full length of the data RAM may be used as the filter length
(160 taps). Though the RCF can calculate only 160 tap filters,
the filter coefficient memory is 256 words long so that more
than one filter configuration can be stored in the memory, and
can be selected using the Coefficient Offset 0xA3 register.
The RCF stores the data from the CIC5 into a 160 ¥ 40 RAM.
160 ¥ 20 is assigned to I data, and 160 ¥ 20 is assigned to Q
data. The RCF uses the RAM as a circular buffer so that it is
difficult to know in which address a particular data element is
stored. To avoid start-up transients due to undefined data RAM
values, the data RAM should be cleared upon initialization.
When the RCF is triggered to calculate a filter output, it starts
by multiplying the oldest value in the data RAM by the first
coefficient, which is pointed to by the RCF Coefficient Offset
register (0xA3). This value is accumulated with the products of
newer data-words multiplied by the subsequent locations in the
coefficient RAM until the coefficient address RCF
is reached.
Coefficient Address
0
1
2 = (N
The RCF Coefficient Offset register can be used for two pur-
poses. The main purpose of this register is allow for multiple
filters to be loaded into memory and selected simply by chang-
ing the offset as a pointer for rapid filter changes. The other use
of this register is to form part of symbol timing adjustment. If
the desired filter length is padded with zeros on the ends, the
starting point can be adjusted to form slight delays in when the
filter is computed with reference to the high speed clock. This
allows for vernier adjustment of the symbol timing. Course
adjustments can be made with the RCF Decimation Phase.
The output rate of this filter is determined by the output rate of
the CIC5 stage and M
RCF Output Scale Factor and Control Register
Register 0xA4 is a compound register and is used to configure
several aspects of the RCF register. Bits 3–0 are used to set the
scale of the fixed-point output mode. This scale value may also
be used to set the floating-point outputs in conjunction with
Bit 6 of this register.
Bits 4 and 5 determine the output mode. Mode 00 sets the chip
up in fixed-point mode. The number of bits is determined by
the parallel or link port configuration.
Mode 01 selects floating-point mode 8 + 4. In this mode, an
8-bit mantissa is followed by a 4-bit exponent. In mode 1x (x
is don’t care), the mode is 12 + 4, or 12-bit mantissa and 4-bit
exponent.
REV. 0
TAPS
– 1)
Table V. Three-Tap Filter
RCF
f
SAMPR
:
Impulse Response
h(0)
h(1)
h(2)
=
f
M
SAMP
RCF
5
OFF
Data
N(0) oldest
N(1)
N(2) newest
+ N
TAPS
– 1
–31–
Normally, the AD6635 will determine the exponent value that
optimizes numerical accuracy. However, if Bit 6 of this control
register is set, the values stored in Bits 3–0 is used to scale the
output. This ensures that consistent scaling and accuracy dur-
ing conditions that may warrant predictable output ranges. If
Bits 3–0 are represented by RCF Scale, then the scaling factor in
dB is given by:
For RCF Scale of 0, the Scaling Factor is equal to
–18.06 dB, and for maximum RCF Scale of 15, the Scaling
Factor is equal to 72.25 dB.
If Bit 7 of this register is set, the same exponent will be used for
both the real and imaginary (I and Q) outputs. The exponent
used will be the one that prevents numeric overflow at the
expense of small signal accuracy. However, this is seldom a
problem, as small numbers would represent 0 regardless of
the exponent used.
Bit 8 of this register is the RCF bank select bit used to program
the register. When this bit is 0, the lowest block of 128 is selected
(taps 0 through 127). When high, the highest block is selected
(taps 128 through 255). It should be noted that while the chip
is computing filters, tap 127 is adjacent to 128 and there are no
paging issues.
Bit 9 of this register selects where the input to each RCF comes
from. If Bit 9 is clear, the RCF input comes from the CIC5
normally associated with the RCF. For Channels 0 through 3, if
the bit is set, the input comes from CIC5 Channel 1. The only
exception is Channel 1, which uses the output of CIC5 from
Channel 0 as its alternate. Using this feature, each RCF can
operate either on its own channel’s NCO + rCIC2 + CIC5 data
or be paired with the RCF of Channel 1. The RCF of Channel 1
can also be paired with Channel 0. This control bit is used with
polyphase distributed filtering.
Similarly for Channels 4 through 7, if the bit is set, the input
comes from CIC5 Channel 5. The only exception is Channel 5,
which uses the output of CIC5 Channel 4 as its alternate source.
If Bit 10 is clear, the AD6635 channel operates in normal
mode. However, if Bit 10 is set, then the RCF is bypassed to
perform Channel BIST. See the Channel BIST (Built-in Self
Test) section below for more details.
Note that the outputs of the RCF can be sent directly to the
output ports (parallel or link) using the appropriate setting in
Port Control register (see Memory Map for Output Port Con-
trol Registers). Alternately, data from more than one channel
can be interleaved into the interpolating half-band filters and
AGCs (even if half-band filters and AGCs are bypassed, inter-
leaving function is still accomplished). This feature to interleave
data internal to the AD6635 allows the usage of multiple chan-
nels to process a single carrier.
Scaling Factor = RCF Scale – 3
Table VI. Output Mode Formats
Floating Point 12 + 4
Floating Point 8 + 4
Fixed Point
(
)
¥
20
1x
01
00
log
AD6635
10
( )
2
dB