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4.2
ELECTRONICS OVERVIEW
Technical Service Manual
4 - 15
430-00587-008 (Rev. 2/05)
The transmitter circuitry consists of a sweep oscillator, a voltage-controlled oscillator
(VCO), and a driver.
The sweep oscillator (ICs U1A and portion of U2, capacitor C5, and resistor R15 through
R18) oscillates at approximately 12 kHz with a 50 percent duty cycle. A CMOS gate within
U2 is used for a quality rail-to-rail symmetrical signal for greater timing accuracy. The
output of the sweep oscillator (C2) is b2 VDC and +3 VDC. The C2 output is used
to sweep the VCO at U2-9.
IC U2, capacitor C7, and resistor R21 constitute the VCO. U2 is originally a phase-lock
loop (PLL) IC with the VCO portion sweeping output frequencies from 4 MHz to 6 MHz.
The VCO center frequency is determined by R21 and C7. Activating either signal,
PROX_AIR_EN or DIST_AIR_EN, enables the VCO.
The driver consists of a push-pull, emitter-follower complementary pair of transistors: Q4
and Q5. The driver supplies input to proximal sensor X1 and distal sensor X2.
The receiver consists of an amplifier, detector, and buffer.
The amplifier consists of transistors Q3, Q6, Q2, and associated passive components. The
amplifier is biased by 2V5REF and is designed for wide power supply range. Q3 is biased
by PROX_AIR_EN in order to receive from proximal sensor X1. Q6 is biased by
DIST_AIR_EN to receive from distal sensor X2.
The detector is an emitter-follower transistor Q1. Q1 allows maximum input impedance.
Capacitor C1 and resistor R4 constitute a time constant of 200 microseconds (µS). Since
the time between peaks is approximately 40 µS, the output (*AIR_OPT) remains high with
a pronounced sawtooth ripple.
The buffer (IC U1A and resistors R7 and R2) also amplifies the detected signal.
The pin detector flex circuitry detects movement of the primary and secondary valve pins
by optical transmitters CR1 and CR2, and optical receivers Q1 and Q2. Light interrupters
are attached to the pins and as the pins move, the appropriate valve movement signals
are transferred to the MCU PWA through the bubble sensor PWA.
Summary of Contents for LifeCare XL Series
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