Datasheet
2.2.3.1 Analog Input Option 1
2.2.3.2 Analog Input Option 2
Circuit Description
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Table 6. Analog Input Jumper description
EVM Banana Description Jumper Setting
Jack
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.
SJP1 AMP OUT+, +v terminal of T1 2-3 → Amp out+ is selected as the source of input to ADC; 1-2 → Use
Analog input from J6 as signal source to ADC (Use with appropriate SJP5
setting)
SJP2 AMP OUT-,–, –v terminal of T1 2-3 → Amp out+ is selected as the source of input to ADC; 1-2 → Ground,
(Default) Also can be used to connect J8 as a differential input along with
SJP1 and SJP3 setting.
SJP3 INPUT –ve select 1-2 → J8 supplies the analog signal to ADC; 2-3 → +ve Input to amplifier.
DEFAULT is No Shunt
SJP5 INPUT +ve select 1-2 → J6 supplies the analog signal to ADC. 2-3 → –ve 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
Option Goal J11 Signal to
ADC
1 Evaluate ADC SJP1 → 1-2; SJP2 → 1-2; SJP3 → Do not connect From J6 default
performance No shunt; SJP5 → 1-2; JP7 → 1-2;
using direct
input to ADC.
2 Evaluate ADC SJP1 → 2-3; SJP2 → 2-3; SJP3 → J9 → 5V, J11 → GND Signal from Used if input signal
performance No shunt; SJP5 → 2-3; JP7 → 2-3; J6 is amplified requires amplification.
using input Install J8; remove R84; by THS4509
through
THS4509
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 7 . 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 ADS6149 data sheet under the recommended input circuit
for high-bandwidth (>100 MHz IF) inputs. However, the recommended low-bandwidth input circuit for the
ADS6149 or the recommended input circuit for the ADS5547 can be easily implemented on the surface
mount pads provided.
Option 2 allows the use of an amplifier to provide input to the ADC. TI has a range of wideband
operational amplifiers such as THS4508/09/11/13/20. On this EVM, THS4509 is used as an example to
amplify the input from J8. The THS4509 is powered up by applying 5 V to J9 and GND to J11. A
differential power supply may also be used to power up the amplifier if common-mode biasing is an issue
for DC-coupled applications. See the THS4509 data sheet (SLOS547 ). The output of the THS4509 is
filtered through a band-pass filter before ADC input. The band-pass filter can be designed depending on
the end application. By default, the band-pass filter components are not populated as the filter design
14 ADS61x9/55xxEVM SLWU061A – December 2008 – Revised June 2009
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