Multivibrator Circuits

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Multivibrator Circuits

• Dr. T.Y. Chang
• NTHU EE

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Contents

• Multivibrator
• Text Book Sedra/Smith V.5 Chapter 11.1

3
Latches and FFs

• Bi-stable

4
RS FF
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Ex 11.1 Determine (W/L) Ratio

• Determine the min. W/L ratios of Q5 and Q6 to
  ensure that the FF will switch
• Given k, Vt, (W/L)Inv
• Sol

Figure 11.4 The relevant portion of the
flip-flop circuit of Fig. 11.3 for determining
the minimum W/L ratios of Q5 and Q6 needed to
ensure that the flip-flop will switch.
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SRAM Cell

• Static Random Access Memory Cell
• Clocked RS FF

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DFFs

• Non-overlapping Clock

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DFFs (Cont.)
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Multivibrator

• Monostable multivibrator (One-shot)
• One stable state
• One quasi-stable state
• Produce a fixed pulse T
• Astable
• No stable state

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RC Charge/Discharge Equation

• V(t)VF - (VF-VS)e-t/(RC)
• Final V Init. V

VF
V
GND
VS
V(t) with init. value
VF
V(t)
VS
time
t
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A CMOS Monostable Circuit

• Protection Diode Circuit and Equivalent Circuit

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Operation Timing Diagram
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At the point of first VIH
1/(j?C)0
Vo1VDDRon/(RRon)
At this moment
?V1VDDR/(RRon)
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At the Duration of Vo1L
V(t)VF - (VF-VS)e-t/(RC)
VI2VDD-(VDD-VDDRon/t) e-t/(tC) Vo1VDDRon/t
e-t/(tC) t RRon
At this duration
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When VI2 reaches Vth
VDDVD1
Fig. 11.14 Circuit that applies during the
discharge of C (at the end of the monostable
pulse interval T).
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Timing Calculation

• Calculate T (and recovery time)
• V(t)VF - (VF-VS)e(-t/RC)

Recovery time
T
V(t)VthVDD -?V1e(-T/tC)
TC(RRon) lnR/(RRon) VDD/(VDD-Vth)
V(t)1.02VDDVDD VD1e(-Trcv/tC)
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Astable Multivibrator

• Calculate T
• V(t)VF - (VF-VS)e(-t/RC)

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Ring Oscillator
Odd Number of Inverters
T2NtP
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Problem (Not HW)

• A multi-vibrator circuit consisted of two
  inverters (logic-1VDD logic-00V threshold Vth
  VDD/2), one resistor with value R and a
  capacitor with value C is connected as follows.
• Two inverters are cascaded in series with three
  nodes A, B, D
• Node A is the 1st inverters input
• Node B is the output of the 1st inverter and also
  the input of 2nd inverter
• Node D is the output of the 2nd inverter
• Resistor R is inserted between nodes A and B
• Capacitor C is inserted between nodes A and D.
• (hint this is an astable multi-vibrator)
• Briefly draw the figure of this scheme
• Show the output waveform in nodes A, B, and D.
• Calculate the period in node D.