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2.2.3 Analog Inputs
The EVM can be configured to use either a transformer-coupled input or a THS4509 amplifier input, both
from a single-ended source. The SMA connector J6 provides the single-ended analog input to the
transformer-coupled input of the ADC. The SMA connector J8 is not installed by default, but can be used
to bring a differential input clock to the transformer-coupled input or to bring a single-ended input to the
THS4509 input circuit. To set the transformer up for one of these options, the EVM must be configured as
per the options listed in Table 7. Prior to making any jumper changes, see the schematic located on the TI
Web site in the relevant ADS41xx or ADS41Bxx product folder.
Table 6. Analog Input Jumper Description
EVM Jumper Description Jumper Setting
options
J6 Analog input single-ended.
J8 Analog input, can be used with J6 Not populated
for differential input
J9 Power supply + Apply 5 V
J11 Power Supply - Ground
R98/106 AMP out+ R106 → Amp out+ is selected as the source of input to ADC; R98 → Use
Analog input from J6 as signal source to ADC
R97/99 AMP out- R99 → Amp out+ is selected as the source of input to ADC; R97 → Use
Analog input from J6 as signal source to ADC
R82/96 -Input select R82 → Differential signal input to transformer T1 (remove R84); R96 →
negative input to amplifier
R94/95 +Input select R94 → single-ended input to transformer T1; R95 → positive input to
amplifier
JP7 Power down for amplifier 2-3 → Pulls up the pin (normal operation or amplifier is ON); 1-2 →
THS4509 Grounds the pin (low-power mode or amplifier is off)
Table 7. EVM Analog Input Options
EVM Evaluation Jumper Changes Required Voltage on J9 and Analog Comments
Options Goal J11 Signal to
ADC
1 Evaluate ADC Install: R84, R94, R97, R98; Do not connect From J6 Default
performance Remove: R82, R95, R96, R99, R106
using direct
input to ADC.
2 Evaluate ADC Install: R95, R96, R99, R106; J9 → 5V, J11 → GND Signal from Used if input signal
performance Remove: R82, R84, R94, R97, R98 J6 is amplified requires amplification.
using input by THS4509
through
THS4509
2.2.3.1 Analog Input Option 1
Option 1 supplies the transformer-coupled input from J6 to ADC. This configuration is the default on the
EVM. The test result using this option is shown in Figure 10. A double-transformer input circuit is used to
provide better differential to single-ended conversion than a single transformer can provide. The
transformers used are both of a 1:1 turns ratio, so termination of the 50-Ω input signal path after the
transformers can be two 25-Ω resistors terminated to the common-mode voltage (VCM) provided by the
ADC.
Following the transformer coupling, surface-mount pads are provided for several input circuits. By default,
the input circuit is configured as shown in the ADS4149 data sheet under the recommended input circuit
for high-bandwidth (>100-MHz IF) inputs. However, the recommended low-bandwidth input circuit for the
ADS4149 can be easily implemented on the surface-mount pads provided.
12
ADS41xx/58B18EVM SLWU067C–November 2009–Revised May 2012
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