ADC14X250 datasheet(42/69 Pages) TI1

42 / 69 page

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100

1000

Frequency [MHz]

No series resistance

10 ohm series resistance

C001

ADC14X250

SLASE49 – DECEMBER 2015

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Figure 41. Measured Differential Impedance of Analog Input Network on a Smith Chart (100

Ω)

9.1.1.3 Input Bandwidth

The input bandwidth of the ADC14X250 device is defined here as the frequency at which the fundamental

amplitude of the sampled data deviates by 3 dB, compared to the amplitude at low frequencies, for a low-

impedance input sinusoidal signal with constant voltage amplitude at the VIN+ and VIN– input pins. The voltage

frequency response is shown in Figure 42.

The peaking in the frequency response is caused by the resonance between the package bond wires and input

capacitance as well as a parasitic 0.5-nH series trace inductance leading to the device pins. This peaking is

typically made insignificant by the stop-band of an anti-aliasing filter that precedes the ADC input. For broadband

applications, 10-

Ω resistors may be put in series with the VIN+ and VIN– input pins. This extra resistance flattens

out the frequency response at the cost of adding some attenuation in the signal path. The additional series

resistance also accordingly modifies the measured SDD11 looking into the analog input.

Figure 42. Measured Input Voltage Frequency Response

ADC14X250 Datasheet(PDF) 42 Page - Texas Instruments