TSA1204

Application information

19/31

8.6

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 proper separate 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 output part is mandatory to prevent

noise from coupling onto the input signal. The best compromise is to connect AGND,

DGND, GNDBI in a common point whereas GNDBE must be isolated. Similarly, the

AVCC, DVCC and VCCBI power supplies must be separate from the VCCBE power

supply.

●

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.

●

All inputs and outputs must be properly terminated with output termination resistors;

then 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.

●

Choose component sizes as small as possible (SMD).

8.7

EVAL1204/BA evaluation board

The EVAL1204/BA is a 4-layer board with high decoupling and grounding level. The

schematic of the evaluation board is shown in Figure 30 and its top overlay view in

Figure 29. The board has been characterized with a fully devoted ADC test bench as shown

in Figure 28.

Figure 28.

Analog-to-digital converter characterization bench

Table 12.

10

20

120

54

Optimized power (mW)

95

120

Sine Wave

Generator

HP8644

ADC

evaluation

board

Pulse

Generator

Logic

Analyzer

Sine Wave

Generator

HP8644

HP8133

Vin

Clk

Data

Clk

PC