AD9446-100LVDS/PCB Analog Devices Inc, AD9446-100LVDS/PCB Datasheet - Page 24

• Manufacturer Part Number: AD9446-100LVDS/PCB
• Description: BOARD EVAL FOR AD9446-100 LVDS
• Manufacturer: Analog Devices Inc

Specifications of AD9446-100LVDS/PCB

• Number Of Adc's: 1
• Number Of Bits: 16
• Sampling Rate (per Second): 100M
• Data Interface: Parallel
• Inputs Per Adc: 1 Single Ended
• Input Range: 2 ~ 4 Vpp
• Power (typ) @ Conditions: 2.6W @ 100MSPS
• Voltage Supply Source: Single
• Operating Temperature: -40°C ~ 85°C
• Utilized Ic / Part: AD9446
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

AD9446
THEORY OF OPERATION
The AD9446 architecture is optimized for high speed and ease
of use. The analog inputs drive an integrated, high bandwidth
track-and-hold circuit that samples the signal prior to quantization
by the 16-bit pipeline ADC core. The device includes an on-board
reference and input logic that accepts TTL, CMOS, or LVPECL
levels. The digital output logic levels are user selectable as standard
3 V CMOS or LVDS (ANSI-644 compatible) via the OUTPUT
MODE pin.
ANALOG INPUT AND REFERENCE OVERVIEW
A stable and accurate 0.5 V band gap voltage reference is built
into the AD9446. The input range can be adjusted by varying
the reference voltage applied to the AD9446, using either the
internal reference or an externally applied reference voltage.
The input span of the ADC tracks reference voltage changes
linearly.
Internal Reference Connection
A comparator within the AD9446 detects the potential at the
SENSE pin and configures the reference into three possible states,
which are summarized in Table 9. If SENSE is grounded, the
reference amplifier switch is connected to the internal resistor
divider (see Figure 55), setting VREF to ~1.6 V. If a resistor
divider is connected as shown in Figure 56, the switch again sets
to the SENSE pin. This puts the reference amplifier in a
noninverting mode with the VREF output defined as
In all reference configurations, REFT and REFB drive the
analog-to-digital conversion core and establish its input span.
The input range of the ADC always equals twice the voltage at
the reference pin for either an internal or an external reference.
Internal Reference Trim
The internal reference voltage is trimmed during the production
test; therefore, there is little advantage to the user supplying an
external voltage reference to the AD9446. The gain trim is per-
formed with the AD9446 input range set to 3.2 V p-p nominal
(SENSE connected to AGND). Because of this trim and the
maximum ac performance provided by the 3.2 V p-p analog
input range, there is little benefit to using analog input ranges
VREF
=
0
5 .
V
×
⎛ +
⎜
⎝
1
R2
R1
⎞
⎟
⎠
Rev. 0 | Page 24 of 36
<2 V p-p. However, reducing the range can improve SFDR
performance in some applications. Likewise, increasing the
range up to 3.8 V p-p can improve SNR. Users are cautioned
that the differential nonlinearity of the ADC varies with the
reference voltage. Configurations that use <2.0 V p-p may
exhibit missing codes and therefore degraded noise and
distortion performance.
10μF
10μF
+
+
0.1μF
0.1μF
SENSE
Figure 56. Programmable Reference Configuration
VREF
VIN+
VIN–
Figure 55. Internal Reference Configuration
R2
SENSE
R1
VREF
VIN+
VIN–
SELECT
LOGIC
SELECT
AD9446
LOGIC
AD9446
0.5V
CORE
0.5V
ADC
CORE
ADC
REFT
REFB
REFT
REFB
0.1μF
0.1μF
0.1μF
0.1μF
0.1μF
0.1μF
+
10μF
+
10μF