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MC143416PB

Dual 16-Bit Linear Codec-Filter

Freescale Semiconductor 

Freescale Semiconductor, Inc.

LAYOUT CONSIDERATIONS

Printed Circuit Board Layout Considerations

The MC143416 is manufactured using high–speed CMOS

VLSI technology to implement the complex analog signal

processing functions of a PCM Codec–Filter. The fully–differ-

ential analog circuit design techniques used for this device

result in superior performance for the switched capacitor fil-

ters, the analog–to–digital converter (ADC) and the digital–

to–analog converter (DAC). Special attention was given to

the design of this device to reduce the sensitivities of noise,

including power supply rejection and susceptibility to radio

frequency noise.

This device was designed for ease of implementation, but

due to the large dynamic range and the noisy nature of the

environment for this device (digital switches, radio tele-

phones, DSP front–end, etc.), special care must be taken to

assure optimum analog transmission performance.

PC Board Mounting

It is recommended that the device be soldered to the PC

board for optimum noise performance. If the device is to be

used in a socket, it should be placed in a low parasitic pin

inductance (generally, low–profile) socket.

Power Supply, Ground, and Noise Considerations

This device is intended to be used in switching applica-

tions which often require plugging the PC board into a rack

with power applied. This is known as “hot–rack insertion”. In

these applications, care should be taken to limit the voltage

on any pin from going positive of the VDD pins, or negative of

the GND pins. One method is to extend the ground and pow-

er contacts of the PCB connector. The device has input

protection on all pins and may source or sink a limited

amount of current without damage. Current limiting may be

accomplished by series resistors between the signal pins

and the connector contacts.

The most important considerations for PCB layout deal

with noise. This includes noise on the power supply, noise

generated by the digital circuitry on the device, and cross–

coupling digital or radio frequency signals into the audio sig-

nals of this device. The best way to prevent noise is to:

• Keep digital signals as far away from audio signals as

possible.

• Keep radio frequency signals as far away from the audio

signals as possible.

• Use short, low inductance traces for the audio circuitry to

reduce inductive, capacitive, and radio frequency noise

sensitivities.

• Use short, low inductance traces for digital and RF

circuitry to reduce inductive, capacitive, and radio

frequency radiated noise.

• Bypass capacitors should be connected from DVDD to

DGND, and VAGREF and VAG to AGND with minimal

trace length. Ceramic monolithic capacitors of about 0.1

µF are acceptable for the DVDD and VAGREF pins to

decouple the device from its own noise. The DVDD

capacitor helps supply the instantaneous currents of the

digital circuitry in addition to decoupling the noise which

may be generated by other sections of the device or

other circuitry on the power supply. The VAGREF

decoupling capacitor is effecting a low–pass filter to

isolate the mid–supply voltage from the power supply

noise generated on–chip, as well as external to the

device. The VAG decoupling capacitor should be about

0.01 µF. This helps to reduce the impedance of the VAG

pin to AGND at frequencies above the bandwidth of the

VAG generator, which reduces the susceptibility to RF

noise.

• Use a short, wide, low inductance trace to connect the

DGND ground pin to the power supply ground. The

DGND pin is the digital ground and the most negative

power supply pin for the analog circuitry. All analog

signal processing is referenced to the VAG pin, but

because digital and RF circuitry will probably be powered

by this same ground, care must be taken to minimize

high frequency noise in the AGND trace. Depending on

the application, a double–sided PCB with a ground plane

connecting all of the digital and analog GND pins

together would be a good grounding method. A

multilayer PC board with a ground plane connecting all

of the digital and analog GND pins together would be the

optimal ground configuration. These methods will result

in the lowest resistance and the lowest inductance in the

ground circuit. This is important to reduce voltage spikes

in the ground circuit resulting from the high–speed digital

current spikes. The magnitude of digitally–induced

voltage spikes may be hundreds of times larger than the

analog signal the device is required to digitize.

• Use a short, wide, low inductance trace to connect the

VDD power supply pin to the 5 V power supply.

Depending on the application, a double–sided PCB with

VDD bypass capacitors to the ground plane, as described

above, may complete the low impedance coupling for the

power supply. For a multilayer PC board with a power

plane, connecting all of the VDD pins to the power plane

would be the optimal power distribution method. The

integrated circuit layout and packaging considerations for

the 5 V VDD power circuit are essentially the same as for

the ground circuit.

MOTOROLA

For More Information On This Product,

Go to: www.freescale.com

MC143416

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