3 V PCM Codec-Filter
Description
MOTOROLA
SEMICONDUCTOR TECHNICAL DATA
Order this document by XC145481/D
XC145481
Product Preview 3 V PCM Codec-Filter
The XC145481 is a general purpose per channel PCM Codec–Filter with pin selectable Mu–Law or A–Law companding, and is offered in 20–pin DIP, SOG, and SSOP packages.
This device performs the voice digitization and reconstruction as well as the band limiting and smoothing required for PCM systems.
This device is designed to operate in both synchronous and asynchronous applications and contains an on–chip precision reference voltage.
This device has an input operational amplifier whose output is the input to the encoder section.
The encoder section immediately low–pass filters the analog signal with an active R–C filter to eliminate very high frequency noise from being modulated down to the passband by the switched capacitor filter.
From the active R–C filter, the analog signal is converted to a differential signal.
From this point, all analog signal processing is done differentially.
This allows processing of an analog signal that is twice the amplitude allowed by a single–ended design, which reduces the significance of noise to both the inverted and non–inverted signal paths.
Another advantage of this differential design is that noise injected via the power supplies is a common–mode signal that is cancelled when the inverted and non–inverted signals are recombined.
This dramatically improves the power supply rejection ratio.
After the differential converter, a differential switched capacitor filter bandpasses the analog signal from 200 Hz to 3400 Hz before the signal is digitized by the differential compressing A/D converter.
The decoder accepts PCM data and expands it using a differential D/A converter.
The output of the D/A is low–pass filtered at 3400 Hz and sinX/X compensated by a differential switched capacitor filter.
The signal is then filtered by an active R–C filter to eliminate the out of band energy of the switched capacitor filter.
The...
Similar Datasheet
