ADS5463

THS9001

AIN

AIN

VIN

VIN

THS9001

S0177-03

1000pF

1000pF

39pF

50 W

50 W

0.1 F

m

1000pF

1000pF

18 H

m

18pF

AIN

AIN

VREF

ADS5463

+5V

THS4509

CM

348 W

348 W

100 W

100 W

78.9 W

78.9 W

49.9 W

VIN

From

50

Source

W

49.9 W

49.9 W

49.9 W

0.1 F

m

0.1 F

m

0.22 F

m

0.22 F

m

0.22 F

m

S0193-02

ADS5463

intermediate-frequencies in the 50-MHz–350-MHz range, the configuration shown in Figure 32 can be used. The

component values can be tuned for different intermediate frequencies. The example shown is located on the

evaluation module and is tuned for an IF of 170 MHz. More information regarding this configuration can be found

in the ADS5463 EVM User Guide (SLAU194) and the THS9001 50 MHz to 350 MHz Cascadeable Amplifier data

sheet (SLOS426).

Figure 32. Using the THS9001 IF Amplifier With the ADS5463

Figure 33. Using the THS4509 With the ADS5463

For applications requiring dc-coupling with the signal source, a differential input/differential output amplifier like

the THS4509 (see Figure 33) provides good harmonic performance and low noise over a wide range of

frequencies. Notice that VREF is used for the common mode with the ADS5463 and ADS5444/5440, whereas

VCM must be used with the ADS5474.

In this configuration, the THS4509 amplifier circuit provides 10 dB of gain, converts the single-ended input to

differential, and sets the proper input common-mode voltage to the ADS5463 by using the VREF pin from the

ADC. The 50-

Ω resistors and 18-pF capacitor between the THS4509 outputs and ADS5463 inputs (along with

the input capacitance of the ADC) limit the bandwidth of the signal to about 70 MHz (–3 dB). Input termination is

accomplished via the 78.9-

Ω resistor and 0.22-

µF capacitor to ground, in conjunction with the input impedance of

the amplifier circuit. A 0.22-

µF capacitor and 49.9-Ω resistor are inserted to ground across the 78.9-Ω resistor

and 0.22-

µF capacitor on the alternate input to balance the circuit. Gain is a function of the source impedance,

termination, and 348-

Ω feedback resistor. See the THS4509 data sheet for further component values to set

proper 50-

Ω termination for other common gains. Because the ADS5463 recommended input common-mode

voltage is 2.4 V, the THS4509 is operated from a single power supply input with V S+ = 5 V and V S– = 0 V

(ground). This maintains maximum headroom on the internal transistors of the THS4509.

18

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