PW0268

􀁺` Operating Voltage: 6 10Vdc single source
􀁺` Operating Frequency: broadband output ranging up to 250KHz
􀁺` Variable R/C Oscillator: compensates for transducer resonate frequency drift due to temperature.
􀁺` High Gain Amplifier: varies with time over 32 steps
􀁺` Integrated Band Pass Filter: reduces external component count
􀁺` Bi-direction I/O Pin: simplifies the control function for transmitting a pulse and receiving an echo
􀁺` An adjustable System Clock: enables the control of, the number of pulses transmitted, the slope of the variable gain amplifier, and the pulse repetition rate.
􀁺` The PW0268 IC is suitable for use in car reversing aids, electronic tape measures and other sonar ranging applications.

The PW0268 ultrasonic sonar ranging IC is ideally suited for echo ranging systems. This chip PW0268 has many design features to enhance its performance and ease of use in this application.

The externally tunable RC Oscillator PW0268 automatically tracks and compensates for the shift of the resonate frequency of the transducer due to temperature changes.

The Fix Gain Preamplifier PW0268 can be tailored to compensate for varying transducer sensitivities. The 32-step Time ontrolled Variable Gain Amplifier slope can be modified by adjusting the frequency of the system clock.

An onboard Comparator converts the analog signal of the returning echo to a TTL level digital signal for use with an external microprocessor.

The integrated Band Pass Filters PW0268 can be adjusted for custom applications by changing a few external components.

The frequency of the System Clock can be adjusted to control other operating parameters of the chip including the transmit pulse width and sample rate.

The I_O pin, (pin 1) is a bi-direction pin and is designed as an open collector connection with an internal pull high esistor. When the I_O pin is being pulled low by an external transistor, the RC oscillator generates a tone burst signal at DRIVER_0 (pin 11), the output driver stage for the transducer. After the transmit pulse, the I_O pin, (pin 1) will again go low if a valid echo signal is detected.

The reflected echo signal is presented to the first stage pre-amplifier through ECHO (pin 10). The gain of pre-amplifier can be adjusted to accommodate transducers with varying sensitivities by changing an external resistor between ECHO (pin 10) and GR_I (pin 9).

The 32 steps time controlled variable gain amplifier input TCG_I (pin7) and output TCG_O (pin 6) is synchronized to start incrementing at the end of control pulse signal I-O, (pin 1) and is reset at the beginning of the next control ulse.

Only a few passive components are needed for the active band pass filter. There are two stages, a low pass, LP_I (pin 5) and LP_O (pin 4) and upper band pass, HP_I (pin 3) to HP_O (pin 2). The center frequency and bandwidth of the filter are chosen based on the type of ultrasonic transducer being used and the specific application.

The amplified echo signal after being filtered is routed to a comparator, which shapes and coverts the analog echo signal into digital signal outputted at I_O (pin 1) for further P handling.

The unique temperature compensating Ultrasonic R/C Oscillator circuitry tracks the resonant frequency drift of the transducer that is causes by environment temperature changes. Simply adding dual diodes and one resistor between DRIVER_O (pin 11) and Ftrace (pin 12) is all that is needed to complete this function.