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Question

# a.    You place different voltage measurement probes as indicated to record the voltage waveforms. Sketch each

of the waveforms V1 through V4 as a function of time (as a timing diagram). Sketch for both cases of i) Small RC time constant, ii) Large RC time constant

b.    Find suitable values for R1 and C1 so that the circuit outputs a 1 MHz signal when the input is a 500 MHz signal. How can you make the duty cycle ~ 50%

c.    Show that this is a versatile circuit (assuming the comparator is ideal) that could be used to double any frequency.

1. You are designing a DNA detection system which uses a LED light source to excite a DNA
microarray chip. This light source is used to produce the ﬂuorescence which will be read
by a ﬂuorescence detection unit consisting of ﬁlters and a CCD camera (See ﬁgure below) I Image analysls Raw images of each chann2| DNA microa rray pattern .. Bright areas indicate you
have a DNA match Scan emitted
ﬂuorescent signal Fig: DNA microarray reader system While designing this system you realize that the LED needs to be pulsed at a frequency of
1 m However, the crystal oscillator that you have purchased could only do 500 m
pulse frequency. To overcome this, you decide to implement a circuit that would essentially
double the frequency of the crystal clock which could then be applied to your LED. You
obtain this circuit schematic (shown in ‘a’) from an online source and decide to implement
this. Here, the input (shown in ‘b’) to this circuit is from the crystal clock producing a
square wave pattern of 500 mﬁequency. V0 0 1m52ms 3ms4ms t/ms (a) (b) input , +3V
R2=10 K12 R3=10 K12

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