Möbius inversion formula: Difference between revisions

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{{refimprove|date=January 2011}}
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A '''multivibrator''' is an [[electronic circuit]] used to implement a variety of simple two-state systems such as [[Electronic oscillator|oscillators]], [[timer]]s and [[flip-flop (electronics)|flip-flop]]s. It is characterized by two [[Electronic amplifier|amplifying devices]] ([[transistor]]s, [[Vacuum tube|electron tubes]] or other devices) cross-coupled by [[resistor]]s or [[capacitor]]s. The name "multivibrator" was initially applied to the free-running oscillator version of the circuit because its output waveform was rich in [[harmonics]].<ref>''Multivibrator'' in ''IEEE Std. 100 Dictionary of Standards Terms 7th ed.'',IEEE Press, 2000 ISBN 0-7381-2601-2 page 718</ref>
There are three types of multivibrator circuits depending on the circuit operation:
 
*'''astable''', in which the circuit is not stable in either [[State (computer science)|state]] —it continually switches from one state to the other. It functions as a [[relaxation oscillator]].
*'''monostable''', in which one of the states is stable, but the other state is unstable (transient). A trigger pulse causes the circuit to enter the unstable state. After entering the unstable state, the circuit will return to the stable state after a set time. Such a circuit is useful for creating a timing period of fixed duration in response to some external event. This circuit is also known as a '''one shot'''.
*'''bistable''', in which the circuit is stable in either state.  It can be flipped from one state to the other by an external trigger pulse.  This circuit is also known as a [[Flip-flop (electronics)|flip flop]].  It can be used to store one [[binary digit|bit]] of information.
 
Multivibrators find applications in a variety of systems where square waves or timed intervals are required. For example, before the advent of low-cost integrated circuits, chains of multivibrators found use as [[frequency divider]]s. A free-running multivibrator with a frequency of one-half to one-tenth of the reference frequency would accurately lock to the reference frequency. This technique was used in early electronic organs, to keep notes of different [[octave]]s accurately in tune. Other applications included early [[television]] systems, where the various line and frame frequencies were kept synchronized by pulses included in the video signal.
 
== History ==
[[Image:Vacuum tube multivibrator calibrating wavemeter 1920.jpg|thumb|upright=1.4|A vacuum tube Abraham-Bloch multivibrator oscillator, France, 1920 ''(small box, left)''.  Its harmonics are being used to calibrate a wavemeter ''(center)''.]]
 
The classic multivibrator circuit (also called a ''plate-coupled multivibrator'') is first described by Henri Abraham and Eugene Bloch in ''Publication 27'' of the French ''Ministère de la Guerre'', and in ''Annales de Physique 12, 252 (1919)''. It is a predecessor of Eccles-Jordan trigger<ref>
William Henry Eccles and Frank Wilfred Jordan, "[http://v3.espacenet.com/origdoc?DB=EPODOC&IDX=GB148582&F=0&QPN=GB148582 Improvements in ionic relays]" British patent number: GB 148582 (filed: 21 June 1918; published: 5 August 1920).
</ref> derived from this circuit a year later.
 
The terminology of multivibrators has been somewhat variable, historically.  For example:
* 1942 – multivibrator implies astable: "The multivibrator circuit (Fig. 7-6) is somewhat similar to the [[flip-flop (electronics)|flip-flop]] circuit, but the coupling from the anode of one valve to the grid of the other is by a condenser only, so that the coupling is not maintained in the steady state."<ref>{{cite book
| title = Electrical counting: with special reference to counting alpha and beta particles
| author = Wilfred Bennett Lewis
| publisher = CUP Archive
| year = 1942
| page = 68
}}</ref>
* 1942 – multivibrator as a particular flip-flop circuit: "Such circuits were known as 'trigger' or 'flip-flop' circuits and were of very great importance. The earliest and best known of these circuits was the multivibrator."<ref>{{cite journal
| journal = The Electrician
| title =
| author =
| volume = 128
| issue =
| publisher =
| pages =
| date = Feb 13, 1942
}}</ref>
* 1943 – flip-flop as one-shot pulse generator: "It should be noted that an essential difference between the two-valve flip-flop and the multivibrator is that the flip-flop has one of the valves biased to cutoff."<ref>{{cite book
| title = Time bases (scanning generators): their design and development, with notes on the cathode ray tube
| author = Owen Standige Puckle and E. B. Moullin
| publisher = Chapman & Hall Ltd
| year = 1943
| page = 51
}}</ref>
* 1949 – monostable as flip-flop: "Monostable multivibrators have also been called 'flip-flops'."<ref>{{cite book
| title = Waveforms
| edition = Vol. 19 of MIT Radiation Lab Series
| author = Britton Chance
| publisher = McGraw-Hill Book Co
| year = 1949
| page = 167
}}</ref>
* 1949 – monostable as flip-flop: "... a flip-flop is a monostable multivibrator and the ordinary multivibrator is an astable multivibrator."<ref>{{cite journal
| journal = Wireless Engineer
| title = Development of Time Bases: The Principles of Known Circuits
| author = O. S. Puckle
| volume = 26
| issue = 1
| publisher = Iliffe Electrical Publications
| pages = 139
| date = Jan 1949
}}</ref>
 
== Astable multivibrator ==
An astable multivibrator is a regenerative circuit consisting of two amplifying stages connected in a positive feedback loop by two capacitive-resistive coupling networks.  The amplifying elements may be junction or field-effect transistors, vacuum tubes, [[operational amplifier]]s, or other types of amplifier. The example diagram shows bipolar junction transistors.
 
The circuit is usually drawn in a symmetric form as a cross-coupled pair. Two output terminals can be defined at the active devices, which will have complementary states; one will have high voltage while the other has low voltage, (except during the brief transitions from one state to the other).
 
===Operation===
[[Image:Transistor Multivibrator.svg|thumbnail|220px|Figure 1: Basic [[Bipolar junction transistor|BJT]] astable multivibrator]]
The circuit has two stable states that change alternatively with maximum transition rate because of the "accelerating" positive feedback. It is implemented by the coupling capacitors that instantly transfer voltage changes because the voltage across a capacitor cannot suddenly change. In each state, one transistor is switched on and the other is switched off. Accordingly, one fully charged capacitor discharges (reverse charges) slowly thus converting the time into an exponentially changing voltage. At the same time, the other empty capacitor quickly charges thus restoring its charge (the first capacitor acts as a time-setting capacitor and the second prepares to play this role in the next state). The circuit operation is based on the fact that the forward-biased base-emitter junction of the switched-on bipolar transistor can provide a path for the capacitor restoration.
 
{{anchor|State 1}}'''State 1 (Q1 is switched on, Q2 is switched off):'''<br>
In the beginning, the capacitor C1 is fully charged (in the previous State 2) to the power supply voltage ''V'' with the polarity shown in Figure 1. Q1 is ''on'' and connects the left-hand positive plate of C1 to ground. As its right-hand negative plate is connected to Q2 base, a maximum negative voltage (-''V'') is applied to Q2 base that keeps Q2 firmly ''off''. C1 begins discharging (reverse charging) via the high-value base resistor R2, so that the voltage of its right-hand plate (and at the base of Q2) is rising from below ground (-''V'') toward +''V''. As Q2 base-emitter junction is backward-biased, it does not conduct, so all the current from R2 goes into C1. Simultaneously, C2 that is fully discharged and even slightly charged to 0.6 V (in the previous State 2) quickly charges via the low-value collector resistor R4 and Q1 forward-biased base-emitter junction (because R4 is less than R2, C2 charges faster than C1). Thus C2 restores its charge and prepares for the next State 2 when it will act as a time-setting capacitor. Q1 is firmly saturated in the beginning by the "forcing" C2 charging current added to R3 current; in the end, only R3 provides the needed input base current. The resistance R3 is chosen small enough to keep Q1 (not deeply) saturated after C2 is fully charged.
 
When the voltage of C1 right-hand plate (Q2 base voltage) becomes positive and reaches 0.6 V, Q2 base-emitter junction begins diverting a part of R2 charging current. Q2 begins conducting and this starts the avalanche-like positive feedback process as follows. Q2 collector voltage begins falling; this change transfers through the fully charged C2 to Q1 base and Q1 begins cutting off. Its collector voltage begins rising; this change transfers back through the almost empty C1 to Q2 base and makes Q2 conduct more thus sustaining the initial input impact on Q2 base. Thus the initial input change circulates along the feedback loop and grows in an avalanche-like manner until finally Q1 switches off and Q2 switches on. The forward-biased Q2 base-emitter junction fixes the voltage of C1 right-hand plate at 0.6 V and does not allow it to continue rising toward +''V''.
 
{{anchor|State 2}}'''State 2 (Q1 is switched off, Q2 is switched on):'''<br>
Now, the capacitor C2 is fully charged (in the previous State 1) to the power supply voltage ''V'' with the polarity shown in Figure 1. Q2 is ''on'' and connects the right-hand positive plate of C2 to ground. As its left-hand negative plate is connected to Q1 base, a maximum negative voltage (-''V'') is applied to Q1 base that keeps Q1 firmly ''off''. C2 begins discharging (reverse charging) via the high-value base resistor R3, so that the voltage of its left-hand plate (and at the base of Q1) is rising from below ground (-''V'') toward +''V''. Simultaneously, C1 that is fully discharged and even slightly charged to 0.6 V (in the previous State 1) quickly charges via the low-value collector resistor R1 and Q2 forward-biased base-emitter junction (because R1 is less than R3, C1 charges faster than C2). Thus C1 restores its charge and prepares for the next State 1 when it will act again as a time-setting capacitor...and so on... (the next explanations are a mirror copy of the second part of Step 1).
 
===Multivibrator frequency===
 
==== Derivation ====
{{unreferenced section|date=January 2011}}
The duration of state 1 (low output) will be related to the time constant ''R''<sub>2</sub>''C''<sub>1</sub> as it depends on the charging of C1, and the duration of state 2 (high output) will be related to the time constant ''R''<sub>3</sub>''C''<sub>2</sub> as it depends on the charging of C2. Because they do not need to be the same, an asymmetric [[duty cycle]] is easily achieved.
 
The voltage on a capacitor with non-zero initial charge is:
 
:<math>
V_\text{cap}(t) = \left[\left(V_\text{capinit} - V_\text{charging}\right) \times e^{-\frac{t}{RC}}\right] + V_\text{charging}
</math>
 
Looking at C2, just before Q2 turns on the left terminal of C2 is at the base-emitter voltage of Q1 (V<sub>BE_Q1</sub>) and the right terminal is at ''V''<sub>CC</sub> ("''V''<sub>CC</sub>" is used here instead of "+''V''" to ease notation). The voltage across C2 is ''V''<sub>CC</sub> minus ''V''<sub>BE_Q1</sub> . The moment after Q2 turns on, the right terminal of C2 is now at 0&nbsp;V which drives the left terminal of C2 to 0&nbsp;V minus (''V''<sub>CC</sub> - ''V''<sub>BE_Q1</sub>) or ''V''<sub>BE_Q1</sub> - ''V''<sub>CC</sub>. From this instant in time, the left terminal of C2 must be charged back up to V<sub>BE_Q1</sub>. How long this takes is half our multivibrator switching time (the other half comes from C1). In the charging capacitor equation above, substituting:
 
:''V''<sub>BE_Q1</sub> for <math>V_\text{cap}(t)</math>
:(''V''<sub>BE_Q1</sub> - ''V''<sub>CC</sub>) for <math>V_\text{capinit}</math>
:''V''<sub>CC</sub> for <math>V_\text{charging}</math>
results in:
 
:<math>
V_{\text{BE}\_\text{Q1}} = \left(\left[\left(V_{\text{BE}\_\text{Q1}} - V_\text{CC}\right) - V_\text{CC}\right] \times e^{-\frac{t}{RC}}\right) + V_\text{CC}
</math>
 
Solving for t results in:
 
:<math>
t = -RC \times \ln\left(\frac{V_{\text{BE}\_\text{Q1}} - V_\text{CC}}{V_{\text{BE}\_\text{Q1}} - 2 V_\text{CC}}\right)
</math>
 
For this circuit to work, V<sub>CC</sub>>>V<sub>BE_Q1</sub> (for example: V<sub>CC</sub>=5&nbsp;V, V<sub>BE_Q1</sub>=0.6&nbsp;V), therefore the equation can be simplified to:
 
:<math>
t = -RC \times \ln\left(\frac{-V_\text{CC}}{-2 V_\text{CC}}\right)
</math>
 
:or
 
:<math>
t = -RC \times \ln\left(\frac{1}{2}\right)
</math>
 
:or
 
:<math>
t = RC \times \ln(2)
</math>
 
The period of each ''half'' of the multivibrator is therefore given by
''t''&nbsp;= ln(2)''RC''.
 
The total period of oscillation is given by:
 
''T'' = ''t''<sub>1</sub> + ''t''<sub>2</sub> = ln(2)''R''<sub>2</sub> ''C''<sub>1</sub> + ln(2)''R''<sub>3</sub> ''C''<sub>2</sub>
 
<math>f = \frac{1}{T}
 
= \frac{1}{\ln(2) \cdot (R_2 C_1 + R_3 C_2)}
 
\approx \frac{1}{0.693 \cdot (R_2 C_1 + R_3 C_2)}</math>
 
where...
* ''f'' is [[frequency]] in [[hertz]].
* ''R''<sub>2</sub> and ''R''<sub>3</sub> are resistor values in ohms.
* ''C''<sub>1</sub> and ''C''<sub>2</sub> are capacitor values in farads.
* ''T'' is the period (In this case, the sum of two period durations).
 
'''For the special case''' where
* ''t''<sub>1</sub> = ''t''<sub>2</sub> (50% duty cycle)
* ''R''<sub>2</sub> = ''R''<sub>3</sub>
* ''C''<sub>1</sub> = ''C''<sub>2</sub>
 
<math>f = \frac{1}{T}
 
= \frac{1}{\ln(2) \cdot 2RC}
 
\approx \frac{0.72}{RC}</math><ref name=Fink75>Donald Fink (ed), ''Electronics Engineers' Handbook'', McGraw Hill, 1975 ISBN 070209804,  page 16-40</ref>
 
==== Output pulse shape ====
 
The output voltage has a shape that approximates a square waveform. It is considered below for the transistor Q1.
 
During [[#State 1|State 1]], Q2 base-emitter junction is reverse-biased and the capacitor C1 is "unhooked" from ground. The output voltage of the switched-on transistor Q1 changes rapidly from high to low since this low-resistive output is loaded by a high impedance load (the series connected capacitor C1 and the high-resistive base resistor R2).
 
During [[#State 2|State 2]], Q2 base-emitter junction is forward-biased and the capacitor C1 is "hooked" to ground. The output voltage of the switched-off transistor Q1 changes exponentially from low to high since this relatively high resistive output is loaded by a low impedance load (the capacitance C1). This is the output voltage of R<sub>1</sub>C<sub>1</sub> integrating circuit.
 
To approach the needed square waveform, the collector resistors have to be low resistance. The base resistors have to be low enough to make the transistors saturate in the end of the restoration (R<sub>B</sub> < β.R<sub>C</sub>).
 
===Initial power-up===
When the circuit is first powered up, neither transistor will be switched on. However, this means that at this stage they will both have high base voltages and therefore a tendency to switch on, and inevitable slight asymmetries will mean that one of the transistors is first to switch on. This will quickly put the circuit into one of the above states, and oscillation will ensue. In practice, oscillation always occurs for practical values of ''R'' and ''C''.
 
However, if the circuit is temporarily held with both bases high, for longer than it takes for both capacitors to charge fully, then the circuit will remain in this stable state, with both bases at 0.6 V, both collectors at 0 V, and both capacitors charged backwards to −0.6 V. This can occur at startup without external intervention, if ''R'' and ''C'' are both very small.
 
===Frequency divider===
An astable multivibrator can be synchronized to an external chain of pulses. A single pair of active devices can be used to divide a reference by a large ratio, however, the stability of the technique is poor owing to the variability of the power supply and the circuit elements; a division ratio of 10, for example, is easy to obtain but not dependable. Chains of bistable flip-flops provide more predictable division, at the cost of more active elements.<ref name=Fink75/>
 
===Protective components===
While not fundamental to circuit operation, [[diode]]s connected in series with the base or emitter of the transistors are required to prevent the base-emitter junction being driven into reverse breakdown when the supply voltage is in excess of the ''V''<sub>eb</sub> breakdown voltage, typically around 5-10 volts for general purpose silicon transistors. In the monostable configuration, only one of the transistors requires protection.
 
==Monostable multivibrator circuit==
 
[[Image:Transistor Monostable.svg|thumbnail|220px|Figure 2: Basic [[Bipolar junction transistor|BJT]] monostable multivibrator.]]
 
[[File:Transistor Bistable interactive animated EN.svg|thumbnail|220px|Figure 3: Basic animated interactive BJT bistable multivibrator circuit (suggested values: ''R1, R2'' = 1 k&Omega; ''R3, R4'' = 10 kΩ).]]
 
In the monostable multivibrator, the one resistive-capacitive network (C<sub>2</sub>-R<sub>3</sub> in figure 1) is replaced by a resistive network (just a resistor). The circuit can be thought as a 1/2 [[#Astable transistor multivibrator circuit|astable multivibrator]]. Q2 collector voltage is the output of the circuit (in contrast to the [[#Astable transistor multivibrator circuit|astable circuit]], it has a perfect square waveform since the output is not loaded by the capacitor).
 
When triggered by an input pulse, a monostable multivibrator will switch to its unstable position for a period of time, and then return to its stable state. The time period monostable multivibrator remains in unstable state is given by ''t''&nbsp;= ln(2)''R''<sub>2</sub>''C''<sub>1</sub>. If repeated application of the input pulse maintains the circuit in the unstable state, it is called a ''retriggerable'' monostable. If further trigger pulses do not affect the period, the circuit is a ''non-retriggerable'' multivibrator.
 
For the circuit in Figure 2, in the stable state Q1 is turned off and Q2 is turned on. It is triggered by zero or negative input signal applied to Q2 base (with the same success it can be triggered by applying a positive input signal through a resistor to Q1 base). As a result, the circuit goes in [[#State 1|State 1]] described above. After elapsing the time, it returns to its stable initial state.
 
==Bistable multivibrator circuit==
 
{{Main|Flip-flop (electronics)}}
 
In the bistable multivibrator, both the resistive-capacitive network are replaced by resistive networks (just resistors or direct coupling).
 
This [[latch (electronics)|latch]] circuit is similar to an astable multivibrator, except that there is no charge or discharge time, due to the absence of capacitors. Hence, when the circuit is switched on, if Q1 is on, its collector is at 0 V. As a result, Q2 gets switched off. This results in more than half +''V'' volts being applied to R4 causing current into the base of Q1, thus keeping it on. Thus, the circuit remains stable in a single state continuously. Similarly, Q2 remains on continuously, if it happens to get switched on first.
 
Switching of state can be done via Set and Reset terminals connected to the bases. For example, if Q2 is on and Set is grounded momentarily, this switches Q2 off, and makes Q1 on. Thus, Set is used to "set" Q1 on, and Reset is used to "reset" it to off state.
 
== See also ==
* [[Blocking oscillator]]
* [[RC circuit#Time-domain considerations|RC circuit]]
* [[Schmitt trigger]]
 
== References ==
 
<references/>
 
==External links==
* [http://www.falstad.com/circuit/e-multivib-a.html Java applets] simulating the multivibrator circuits.
 
[[Category:Oscillators]]
[[Category:Digital circuits]]
[[Category:Analog circuits]]

Latest revision as of 04:53, 14 July 2014

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DAMIANA – Damiana is found primarily in Central and South America. When a man is confident and has high self-esteem, he often finds that the rest of his life falls into place easily. Inadequate zinc levels block the pituitary gland from releasing lutein and follicle stimulation of hormone which stimulates the production of testosterone. You can even enhance your sexual performance by increasing your staying power. In short, it can be said that as level of testosterone declines, the body starts going back to pre-puberty stage.

You may be debating in your mind where you may be wondering whether they really work. If it says "use for a maximum of 4 hours daily", never go beyond that. Where to find the ingredients that promote penis sensitivity. As far as Bieber's penis enlargement goes, this lawsuit was filed in Michigan by someone who claims they are Selena Gomez's father. When you're dodging sex because you're unhappy with the size of your penis, not only are you passing up opportunities for personal fulfillment, but you're also denying yourself the sexual satisfaction you deserve.

" If he is not brash ancient enough, this affliction can be "Definitive". It is unlike a case where you will be forced to use extenders or surgeries which will expose you to different side effects. And, as advised above, the implications can sometimes be pretty dire. Yohimbine helps impotence caused by poor circulation and emotional problems resulting in raising your testosterone levels and your libido. The science behind these penis enlargement devices consist of enlarging your corpora cavernosa (set of chambers in the penis), so that it can hold more blood, hence making your penis bigger, wider, and harder during erections.

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