AD9963 Analog Devices, AD9963 Datasheet - Page 35

• Manufacturer Part Number: AD9963
• Description: 10-/12-Bit, Low Power, Broadband MxFE
• Manufacturer: Analog Devices

Specifications of AD9963

• Resolution (bits): 12bit
• Throughput Rate: 100MSPS
• # Chan: 2
• Supply V: Multi(+1.8Anlg, +1.8Dig),Multi(+1.8Anlg, +3.3Dig) ,Single(+1.8),Single(+3.3)
• Sample Rate: 100MSPS
• Adc Bits X #adcs-speed: 12x2-100 MHz
• Dac Bits X #dacs-clkspeed: 12x2-170 MHz
• Pkg Type: CSP
• Primary Application: Broadband Wireless

RECEIVE PATH
Rx Path General Description
The AD9961/AD9963 Rx paths consist of dual, differential
input, 100 MSPS ADCs followed by an optional 2× decimation
filter. The Rx path also has digital offset and gain adjustments.
RXQN
The dual ADC paths share the same clocking and reference
circuitry to provide optimal matching characteristics. The
ADCs have a multistage differential pipelined switched
capacitor architecture with output error correction logic. The
ADCs support IF sampling frequencies up to 140 MHz, making
them suitable for undersampling receivers. Also, one of the
ADCs can be powered down and the digital interface can be
placed into single ADC mode. This flexibility makes the part
well-suited for sampling real signals as well.
RECEIVE ADC OPERATION
The Rx path analog inputs look into a nominal differential
impedance of 4 kΩ. The Rx inputs are self-biasing, so they can
be either ac-coupled or direct coupled. The nominal dc bias
level of the inputs is 1.4 volts. A buffered version of the bias
voltage is available at the RXCML pin. This voltage can be used
for biasing external buffer circuits when dc coupling is required.
For optimal dynamic performance, the analog inputs should be
driven differentially. The source impedances driving the Rx
inputs should be matched so that common-mode settling errors
are symmetrical. The Rx inputs can be driven with a single-
ended source, but SNR and SINAD performance is degraded.
ADC Reference Voltage
An internal differential voltage reference creates positive and
negative reference voltages that define the full-scale input
voltage of the ADCs. This full-scale input voltage range can be
adjusted by means of the RX_FSADJ[4:0] parameter in
configuration Register 0x7D. See the Configuration Registers
section for more details on setting the voltage.
The nominal input voltage range is 1.56 V. In general, a tradeoff
can be made between linearity and SNR. Increasing the input
voltage range leads to higher SNR. Decreasing the input voltage
range leads to better linearity.
RXQP
RXIN
RXIP
Q ADC
I ADC
Q OFFSET
I OFFSET
Figure 39. Receive Path Block Diagram
DECIMATION
LPF
LPF
1/2
1/2
SCALE
ASSEMBLER
DATA
TRXD[11:0]
TRXIQ
TRXCLK
Rev. 0 | Page 35 of 60
RXBIAS
The AD9961/AD9963 provide the user with the option to place
a 10 kΩ resistor between the RXBIAS pin and ground. This
resistor is used to set the master current reference of the ADC
core. The RXBIAS resistor should have a tolerance of 1% or
better to preserve the accuracy of the ADC full-scale range.
Care should be taken in the layout to avoid any noise from
coupling into the RXBIAS pin.
RXCML
The RXCML pin of the AD9961/AD9963 provides the user with
a buffered version of the expected ADC common-mode bias
voltage. The RXCML output nominally is at 1.4 V. Bypassing
the RXCML output to analog ground maintains the stability of
the output buffer and lowers the noise. To maintain the
accuracy of the RXCML bias voltage, the current draw from the
pin should be kept below 1 mA.
Differential Input Configurations
Optimum performance is achieved by driving the analog inputs
in a differential input configuration. For baseband applications,
the
and a flexible interface to the ADC.
Figure 41 shows an ac-coupled input configuration. The VOCM
pin should be connected to a voltage that provides sufficient
headroom for the output driver of the differential amp. Usually,
setting VOCM to ½ of the amplifier supply voltage is the optimal
setting. Placing source resistance in series with the amplifiers
outputs isolates the amplifier from on-board parasitic capacitances
and leads to more stable operation.
ADA4937
RXCML
RXQN
RXQP
RXIP
RXIN
Figure 40. Simplified Schematic of Rx Path Inputs
differential driver provides excellent performance
AD9961/AD9963
2kΩ
2kΩ
2kΩ
2kΩ
~1.4V
REG 0x0F[1]
EN
REG 0x7E[0]
CMBIAS
IADC
PD
QADC
AD9961/AD9963
~1.4V