Default Operation And Jumper Selection Settings - Analog Devices AD6642 User Manual

Evaluation Board User Guide
DEFAULT OPERATION AND JUMPER SELECTION
SETTINGS
This section explains the default and optional settings or modes
allowed on the AD6642/AD6657
Power Circuitry
Connect the switching power supply that is supplied in the
evaluation kit between a rated 100 V ac to 240 V ac wall outlet
at 47 Hz to 63 Hz and P201.
Analog Input
The A and B channel inputs on the evaluation board are set up for
a double balun-coupled analog input with a 50 Ω impedance. This
input network is optimized to support a wide frequency band. See
the AD6642 and AD6657 data sheets for additional information on
the recommended networks for different input frequency ranges.
The nominal input drive level is 10 dBm to achieve 2 V p-p full
scale into 50 Ω. At higher input frequencies, slightly higher input
drive levels are required due to losses in the front-end network.
Optionally, Channel A and Channel B inputs on the board can
be configured to use the ADL5562
differential amplifier. The ADL5562 components are included on
the evaluation board at U501 and U502. However, the path into
and out of the ADL5562 can be configured in many different ways
depending on the application; therefore, the parts in the input
and output path are left unpopulated. The user should see the
ADL5562 data sheet for additional information on this part and
for configuring the inputs and outputs. The ADL5562 by default
is held in power-down mode but can be enabled by adding a
jumper on P501 (Channel A) or P502 (Channel B). The ADL5562,
on the Channel A and Channel B inputs, can also be substituted
with the ADA4937 or the ADA4938
parts with the ADC.
The Channel C and Channel D inputs are set up with an optional
input path through the AD8376
(DVGA). Similar to Channel A and Channel B, the amplifier is
included on the board at U601; however, the input-/output-related
components are not included. The user should see the AD8376
data sheet for additional information on this part and for
configuring the inputs and outputs. The AD8376 channels are
also normally held in power-down mode and can be enabled by
adding a jumper on P602 (Channel C) or P601 (Channel D).
Rev. B evaluation board.
ultralow distortion RF/IF
to allow evaluation of these
digitally variable gain amplifier
2V p-p
P S S
A
Figure 3. Default Analog Input Configuration of the AD6642/AD6657
Clock Circuitry
The default clock input circuit that is populated on the
AD6642/AD6657 evaluation board uses a simple transformer-
coupled circuit using a high bandwidth 1:1 impedance ratio
transformer (T701) that adds a very low amount of jitter to the
clock path. The clock input is 50 Ω terminated and ac-coupled
to handle single-ended sine wave types of inputs. The transformer
converts the single-ended input to a differential signal that is
clipped by CR701 before entering the ADC clock inputs.
The board is set by default to use an external clock generator. An
external clock source capable of driving a 50 Ω terminated input
should be connected to J702.
A differential LVPECL clock driver output can also be used to
clock the ADC input using the
AD9517 into the clock path, populate R727 and R728 with 0 Ω
resistors and remove R713 and R714 to disconnect the default clock
path inputs. In addition, populate R817 and R816 with 0 Ω
resistors and remove R815 and R818 to disconnect the default
clock path outputs and insert the AD9517 LVPECL Output 1. The
AD9517 must be configured through the SPI controller software to
set up the PLL and other operation modes. Consult the AD9517
data sheet for more information about these and other options.
PDWN
To enable the power-down feature, add a shorting jumper across
P702 at Pin 1 and Pin 2 to connect the PDWN pin to AVDD.
NSR
To enable the noise shaping requantizer (NSR) feature, add a
shorting jumper across P701 at Pin 1 and Pin 2 to connect the
NSR ON pin to GND. The NSR feature can also be enabled via
the SPI interface by writing to Register 0x3C. Writing to Bit 4
allows the user to ignore the MODE pin and enable the NSR via
SPI control.
8.2pF
0.1µF 49.9Ω
33Ω
36Ω
P
8.2pF
0.1µF
36Ω
0.1µF
33Ω
49.9Ω
8.2pF
Rev. 0 | Page 5 of 32
AD9517 (U901). To place the
VIN+
AD6642/AD6657
VCM
VIN–
UG-232