Understanding a simple circuit

[hobby_85]

Hey,

I am trying to breakdown this circuit and understand every bit of it before i build it again. The picture is attached. Its an ultrasonic transmitter circuit. An explanation was given as well.

"The ultrasonic transmitter submodule drives a 40kHz piezo-electric open-air ultrasonic transmitter at 12 V [102]. Under software control, this submodule generates ultrasonic pulses of duration 125 μs. The voltage multiplier module generates 12 V from the 3 V supply voltage to drive the ultrasonic transmitter".

I guess the part i don't quite understand is the generation of 12v from 3v. Where does the 12v come from...I dont see another power source in the circuit. btw, US_OUT and US_OUT_EN goes into a Micro-controller, which generates pulses. Dont know exactly what does what yet, but i think US_OUT prolly generates pulses which compares it to the LM8261's SHDN/2...like a comparator. According to the datasheet for MAX864, SHDN = Vin Thats what im understanding. So wheres the 12v?

Also, I wanna build this transmitter, but the MAX864 does'nt come in PDIP. Is there any other similar charge pump with SHDN that comes in PDIP?

Thanks heaps.

 

[crutschow]

What do you think the MAX864 does? Just Google it.

 

[hobby_85]

I did. "The charge pump first doubles the input voltage, then inverts the doubled voltage". From the configuration, I figured it provides the LM8261 with a +Vin and -Vin. And the 12v?

 

[crutschow]

I did. "The charge pump first doubles the input voltage, then inverts the doubled voltage". From the configuration, I figured it provides the LM8261 with a +Vin and -Vin. And the 12v?

It's the output of the op amp driving the transducer. Apparently they are using peak-to-peak voltage in their description.