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TC1026CEOA bảng dữ liệu(PDF) 6 Page - Microchip Technology |
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TC1026CEOA bảng dữ liệu(HTML) 6 Page - Microchip Technology |
6 / 18 page TC1026 DS21725B-page 6 © 2002 Microchip Technology Inc. FIGURE 4-1: COMPARATOR EXTERNAL HYSTERESIS CONFIGURATION 4.2 Precision Battery Monitor Figure 4-2 is a precision battery low/battery dead monitoring circuit. Typically, the battery low output warns the user that a battery dead condition is imminent. Battery dead typically initiates a forced shutdown to prevent operation at low internal supply voltages (which can cause unstable system operation). The circuit of Figure 4-2 uses two TC1026 devices and only six external resistors. AMP 1 is a simple buffer while CMPTR1 and CMPTR2 provide precision voltage detection using VR as a reference. Resistors R2 and R4 set the detection threshold for BATT LOW while resistors R1and R3 set the detection threshold for BATT FAIL. The component values shown assert BATT LOW at 2.2V (typical) and BATT FAIL at 2.0V (typical). Total current consumed by this circuit is typically 28 µA at 3V. Resistors R5 and R6 provide hysteresis for comparators CMPTR1 and CMPTR2, respectively. 4.3 Voice Band Receive Filter The majority of spectral energy for human voices is 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 that is matched to the human voice spectrum can be implemented using Microchip’s CMOS op amps. Figure 4-3 shows a unity-gain multi- pole Butterworth filter with ripple less than 0.15dB in the human voice band. The lower 3dB cut-off frequency is 70Hz (single-order response), while the upper cut-off frequency is 3.5kHz (fourth-order response). 4.4 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 4-4 shows a high Q (30) first order SAT detection bandpass filter using Microchip’s CMOS op amp architecture. This circuit nulls all frequencies except the three SAT tones of interest. + – VR VDD VOUT VSRC RA RB RC TC1026 Comparator TC1026 |
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