本次加拿大代寫主要為asynchronous serial interface相關的Lab
In this lab you will build an oscillator andmakemea-
surements using an oscilloscope.
The oscillator uses a Schmitt trigger inverter. This
type of inverter uses feedback to increase the input
threshold when the output is high and decrease it
when the output is low. This is called “hysteresis”
and one application is to prevent noise from causing
multiple undesired changes in the output when a sig-
nal crosses the input switching threshold.
The following schematic shows the circuit youwill
be measuring at the test points TP1 through TP4:
The first Schmitt trigger inverter is configured as
an oscillator. When the output of the inverter is high,
the capacitor charges up through a 1k resistor and
the Schottky diode until it crosses the upper switch-
ing threshold (?? ??+). Then the output switches off
and discharges the capacitor through both 1k resis-
tors in series until the input crosses the lower switch-
ing threshold (?? ???). The different charge and dis-
charge rates produce an asymmetrical waveform.
The RC circuit at the output of the second inverter
increases the rise time of the signal so it can be mea-
sured by the AD2.
This oscillator’s frequency depends on switching
thresholds and supply voltage, which are difficult to
maintain accurately. However, this oscillator has no
start-up delay and can be integrated into an IC. Thus
this type of oscillator is used when start-up time and
cost are more important than frequency accuracy.