AD6636CBCZ Analog Devices Inc, AD6636CBCZ Datasheet - Page 28

• Manufacturer Part Number: AD6636CBCZ
• Description: IC DIGITAL DWNCONV 4CH 256CSPBGA
• Manufacturer: Analog Devices Inc
• Series: AD6636r

Specifications of AD6636CBCZ

• Rf Type: Cellular, CDMA2000, EDGE, GPRS, GSM
• Number Of Mixers: 1
• Secondary Attributes: Down Converter
• Current - Supply: 450mA
• Voltage - Supply: 3 V ~ 3.6 V
• Package / Case: 256-CSPBGA
• Brief Features: 4/6 Independent Wideband Processing Channel, Quadrature Correction & DC Correction For Complex Input
• Supply Voltage Range: 1.7V To 1.9V
• Operating Temperature Range: -40°C To +85°C
• Ic Function: Digital Down Converter (DDC)
• Rohs Compliant: Yes
• Pin Count: 256
• Screening Level: Industrial
• Package Type: CSPBGA
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Frequency: -
• Gain: -
• Noise Figure: -
• Lead Free Status / Rohs Status: Compliant

AD6636
For example, if the carrier frequency is 100 MHz and the clock
frequency is 80 MHz,
This, in turn, converts to 0x4000 0000 in the 32-bit twos
complement representation for NCO_FREQ.
If the carrier frequency is 70 MHz and the clock frequency is
80 MHz,
This, in turn, converts to 0xE000 0000 in the twos complement
32-bit representation.
Mixer
The NCO is accompanied by a mixer. Its operation is similar to
an analog mixer. It does the down-conversion of input signals
(real or complex) by using the NCO frequency as a local
oscillator. For real input signals, this mixer performs a real
mixer operation (with two multipliers). For complex input
signals, the mixer performs a complex mixer operation (with
four multipliers). The mixer adjusts its operation based on the
input signal (real or complex) provided to each individual
channel.
Bypass
The NCO and the mixer can be bypassed individually in each
channel by writing Logic 1 in the NCO bypass bit in the NCO
control register of the channel under consideration. When
bypassed, down-conversion is not performed and the AD6636
mod
mod
–fs/2
–fs/2
SIGNAL OF INTEREST IMAGE
(
(
f
f
f
f
clk
clk
ch
ch
–7fs/16
–7fs/16
,
,
f
f
clk
clk
)
)
=
=
–3fs/8
–3fs/8
10
20
80
80
=
=
0.25
0.125
–5fs/16
–5fs/16
–fs/4
–fs/4
FREQUENCY TRANSLATION (SINGLE 1MHz CHANNEL TUNED TO BASEBAND)
AFTER FREQUENCY TRANSLATION
WIDEBAND INPUT SPECTRUM (–fsample/2
Figure 30. Frequency Translation Principle Using the NCO and Mixer
WIDEBAND INPUT SPECTRUM (30MHz FROM HIGH SPEED ADC)
–3fs/16
–3fs/16
SIGNAL OF INTEREST
–fs/8
–fs/8
–fs/16
–fs/16
Rev. A | Page 28 of 80
DC
DC
fs/16
fs/16
channel functions simply as a real filter on complex data. This is
useful for baseband sampling applications in which the input
Port A (or C) is connected to the I signal path within the filter
and the Input Port B (or D) is connected to the Q signal path.
This can be desired if the digitized signal has already been
converted to baseband in prior analog stages or by other digital
preprocessing.
Clear Phase Accumulator on Hop
When the clear NCO accumulator bit of the NCO control
register is set (Logic 1), the NCO phase accumulator is cleared
prior to a frequency hop. See the Chip Synchronization section
for details on frequency hopping. This ensures a consistent
phase of the NCO on each hop. The NCO phase offset is
unaffected by this setting and is still in effect. If phase-
continuous hopping is needed, this bit should be cleared (NCO
accumulator is not cleared). The last phase in the NCO phase
register is the initiating point for the new frequency.
Phase Dither
The AD6636 provides a phase dither option for improving the
spurious performance of the NCO. Writing Logic 1 in the phase
dither enable bit of the NCO control register of the individual
channels enables phase dither. When phase dither is enabled,
random phase is added to the LSBs of the phase accumulator of
the NCO. When phase dither is enabled, spurs due to phase
truncation in the NCO are randomized.
The energy from these spurs is spread into the noise floor and
the spurious-free dynamic range is increased at the expense of a
very slight decrease in the SNR. The choice of whether to use
phase dither in a system is ultimately decided by the system
goals. If lower spurs are desired at the expense of a slightly
NCO TUNES SIGNAL TO
SIGNAL OF INTEREST IMAGE
TO +
fs/8
fs/8
fsample/2)
3fs/16
3fs/16
fs/4
fs/4
5fs/16
5fs/16
SIGNAL OF INTEREST
3fs/8
3fs/8
7fs/16
7fs/16
fs/2
fs/2