AD6634BBCZ Analog Devices Inc, AD6634BBCZ Datasheet - Page 22

• Manufacturer Part Number: AD6634BBCZ
• Description: Pb-free Quad Receive Signal Processor
• Manufacturer: Analog Devices Inc
• Series: AD6634r

Specifications of AD6634BBCZ

• Rf Type: Cellular, CDMA2000, EDGE, GPRS, GSM
• Number Of Mixers: 1
• Voltage - Supply: 3 V ~ 3.6 V
• Package / Case: 196-CSPBGA
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Supply: -
• Frequency: -
• Gain: -
• Noise Figure: -
• Secondary Attributes: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD6634
Scaling with Floating-Point or Gain-Ranging ADCs
An example of the exponent control feature combines the AD6600
and the AD6634. The AD6600 is an 11-bit ADC with three bits
of gain ranging. In effect, the 11-bit ADC provides the mantissa,
and the three bits of relative signal strength indicator (RSSI) for
the exponent. Only five of the eight available steps are used by
the AD6600. See the AD6600 data sheet for additional details.
For gain-ranging ADCs such as the AD6600,
where, IN is the value of IN[13:0], EXP is the value of
EXP[2:0], and rCIC2 is the rCIC scale register value (0x92
Bits 9–5 and 4–0).
The RSSI output of the AD6600 numerically grows with increas-
ing signal strength of the analog input (RSSI = 5 for a large
signal, RSSI = 0 for a small signal). When the Exponent Invert
Bit (ExpInv) is set to zero, the AD6634 will consider the small-
est signal at the IN[13:0] to be the largest and as the EXP word
increases, it shifts the data down internally (EXP = 5 will shift a
14-bit word right by five internal bits before passing the data to
the rCIC2). In this example where ExpInv = 0, the AD6634
regards the largest signal possible on the AD6600 as the small-
est signal. Thus, we can use the Exponent Invert Bit to make
the AD6634 exponent agree with the AD6600 RSSI. By setting
ExpInv = 1, this forces the AD6634 to shift the data up (left)
for growing EXP instead of down. The exponent invert bit
should always be set high for use with the AD6600.
The exponent offset is used to shift the data up. For example,
Table I shows that with no rCIC2 scaling, 12 dB of range is lost
when the ADC input is at the largest level. This is undesirable
because it lowers the dynamic range and SNR of the system by reduc-
ing the signal of interest relative to the quantization noise floor.
To avoid this automatic attenuation of the full-scale ADC signal
the ExpOff is used to move the largest signal (RSSI = 5) up to
the point where there is no down shift. In other words, once the
Exponent Invert bit has been set, the exponent offset should be
adjusted so that mod(7–5 + ExpOff, 32) = 0. This is the case
when exponent offset is set to 30 since mod(32, 32) = 0.
Table II illustrates the use of ExpInv and ExpOff when used
with the AD6600 ADC.
Figure 28. Typical Interconnection of the AD6640
Fixed Point ADC and the AD6634
SCALED INPUT
EXPINV
_
=
D11 (MSB)
AD6640
1
D0 (LSB)
,
EXPWEIGHT
VDD
=
IN
×
EXP 2
EXP 1
EXP 0
IN 13
IN 2
IN 1
IN 0
2
AD6634
–
MOD
=
0
(
7
IEN
–
EXP
+
rCIC
2 32
,
)
,
–22–
ADC Input
Level
Largest
Smallest
(ExpInv = 1, rCIC2 Scale = 0)
ADC Input
Level
Largest
Smallest
(ExpInv = 1, ExpOff = 30, ExpWeight = 0)
This flexibility in handling the exponent allows the AD6634 to
interface with gain-ranging ADCs other than the AD6600. The
Exponent Offset can be adjusted to allow up to seven RSSI(EXP)
ranges to be used as opposed to the AD6600’s five. It also allows
the AD6634 to be tailored in a system that employs the AD6600
but does not utilize all of its signal range. For example, if only
the first four RSSI ranges are expected to occur, the ExpOff
could be adjusted to 29, which would then make RSSI = 4
correspond to the 0 dB point of the AD6634.
NUMERICALLY CONTROLLED OSCILLATOR
Frequency Translation
This processing stage comprises a digital tuner consisting of two
multipliers and a 32-bit complex NCO. Each channel of the
AD6634 has an independent NCO. The NCO serves as a quadra-
ture local oscillator capable of producing an NCO frequency
between –CLK/2 and +CLK/2 with a resolution of CLK/2
the complex mode. The worst-case spurious signal from the
NCO is better than –100 dBc for all output frequencies.
Figure 29. Typical Interconnection of the AD6600
Gain-Ranging ADC and the AD6634
Table II. AD6600 Transfer Function with AD6620
ExpInv = 1, and ExpOff = 6
Table I. AD6600 Transfer Function with AD6634
ExpInv = 1, and No ExpOff
AD6600
RSSI[2:0]
101 (5)
100 (4)
011 (3)
010 (2)
001 (1)
000 (0)
AD6600
RSSI[2:0]
101 (5)
100 (4)
011 (3)
010 (2)
001 (1)
000 (0)
AB_OUT
D10 (MSB)
AD6600
D0 (LSB)
RSSI 2
RSSI 1
RSSI 0
AD6634
Data
/4 (>> 2)
/8 (>>3)
/16 (>> 4)
/32 (>> 5)
/64 (>> 6)
/128 (>> 7)
AD6634
Data
/1 (>> 0)
/2 (>> 1)
/4 (>> 2)
/8 (>> 3)
/16 (>> 4)
/32 (>> 5)
EXP 2
EXP 1
EXP 0
IN 13
IN 2
IN 1
IN 0
AD6634
IEN
Signal
Reduction (dB)
–12
–18
–24
–30
–36
–42
Signal
Reduction (dB)
–6
–12
–18
–24
–30
0
REV. 0
32
in