TC1029
DS21340B-page 4
2002 Microchip Technology Inc.
3.0
DETAILED DESCRIPTION
The TC1029 is one of a series of very low power, linear
building block products for low voltage single supply
operations. The TC1029 contains two rail to rail op
amps which operate down to 1.8V with a maximum
supply current of 16
A. The amplifier's input range
extends beyond both supplies by 200mV and the
outputs will swing to within several millivolts of the
supplies, depending on the load current being driven.
The amplifier design is such that large signal gain, slew
rate and bandwidth are largely independent of supply
voltage. The low input bias current and offset voltage of
the TC1029 make it suitable for precision applications.
4.0
TYPICAL APPLICATIONS
The TC1029 lends itself to a wide variety of
applications, particularly in battery powered systems. It
typically finds application in power management,
processor supervisory and interface circuitry.
4.1
Voice Band Receive Filter
The majority of spectral energy for human voices is
found to be in a 2.7kHz frequency band from 300Hz to
3kHz. To properly recover a voice signal in applications
such as radios, cellular phones and voice pagers, a low
power bandpass filter matched to the human voice
spectrum can be implemented, using Microchip’s
CMOS op amps. Figure 4-1 shows a unity gain multi-
pole Butterworth filter with ripple less than 0.15dB in
the human voice band. The lower 3 dB cut-off
frequency is 70Hz (single order response), while the
upper cut-off frequency is 3.5kHz (fourth order
response).
4.2
Supervisory Audio Tone (SAT)
Filter for Cellular
Supervisory Audio Tones (SAT) provide a reliable
transmission path between cellular subscriber units
and base stations. The SAT tone functions much like
the current/voltage used in land line telephone systems
to indicate that a phone is off the hook. The SAT tone
may be one of three frequencies: 5970, 6000 or
6030Hz. A loss of SAT implies that channel conditions
are impaired and if SAT is interrupted for more than 5
seconds a cellular call is terminated.
Figure 4-2 shows high Q (30) second order SAT
detection bandpass filter using Microchip’s CMOS op
amp architecture. This circuit nulls all frequencies
except the three SAT tones of interest.