RHF1401

Application information

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7.6

PCB layout precautions

To use the ADC circuits most efficiently at high frequencies, some precautions have to be

taken for power supplies:

●

First of all, the implementation of 4 separate proper supplies and ground planes

(analog, digital, internal and external buffer ones) on the PCB is recommended for high

speed circuit applications to provide low-inductance and low-resistance common

return.

●

The separation of the analog signal from the digital part and from the buffers power

supply is essential to prevent noise from coupling onto the input signal.

●

Power supply bypass capacitors must be placed as close as possible to the IC pins in

order to improve high frequency bypassing and reduce harmonic distortion.

●

Proper termination of all inputs and outputs is needed; with output termination

resistors, the amplifier load is resistive only and the stability of the amplifier is improved.

All leads must be wide and as short as possible especially for the analog input in order

to decrease parasitic capacitance and inductance.

●

To keep the capacitive loading as low as possible at digital outputs, short lead lengths

of routing are essential to minimize currents when the output changes. To minimize this

output capacitance, use buffers or latches close to the output pins. It is also helpful to

use 47

Ω to 56 Ω series resistors at the ADC output pins, located as close to the ADC

output pins as possible.

●

Choose component sizes as small as possible (SMD).