The MC14LC5480 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, SOIC, SSOP, and TSSOP 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
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 band-passes 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
The MC14LC5480 PCM Codec-Filter accepts a variety of clock formats,
including Short Frame Sync, Long Frame Sync, IDL, and GCI timing
environments. This device also maintains compatibility with Our telecommunication products.
The MC14LC5480 PCM Codec-Filter utilizes CMOS due to its reliable
low-power performance and proven capability for complex analog/digital VLSI functions.