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• • Recognise that oscillators consist of 3 essential parts. |
• • Describe the essential parts of an oscillator. |
• • State the reasons for using positive feedback. |
• • State methods of frequency control in oscillators |
• • State reasons for amplitude control oscillators |
Fig. 1.1.1 The Essential Elements of an Oscillator |
Parts of an Oscillator |
Most oscillators consist of three basic parts: |
1. An amplifier. This will usually be a voltage amplifier and may be biased in class A, B or C. |
2. A wave shaping network. This consists of passive components such as filter circuits that are responsible for the shape and frequency of the wave produced. |
3. A POSITIVE feedback path. Part of the output signal is fed back to the amplifier input in such a way that the feed back signal is regenerated, re-amplified and fed back again to maintain a constant output signal. |
Commonly an oscillator is constructed from an amplifier that has part of its output signal fed back to its input. This is done in such a way as to keep the amplifier producing a signal without the need for any external signal input as shown in Fig. 1.1.1. It can also be thought of as a way of converting a DC supply int... |
Positive feedback. |
The feedback in the amplifier section of an oscillator must be POSITIVE FEEDBACK. This is the condition where a fraction of the amplifier's output signal is fed back to be in phase with the input, and by adding together the feedback and input signals, the amplitude of the input signal is increased. For example, a commo... |
The result of a small amount of positive feedback in amplifiers is higher gain, though at the cost of increased noise and distortion. If the amount of positive feedback is large enough however, the result is oscillation, where the amplifier circuit produces its own signal. |
Using Positive Feedback. |
When an amplifier is operated without feedback it is operating in "open loop" mode. With feedback (either positive or negative) it is in "closed loop" mode. In ordinary amplifiers negative feedback is used to provide advantages in bandwidth, distortion and noise generation, and in these circuits the closed loop gain of... |
In oscillators using positive feedback it is important that amplitude of the oscillator output remains stable. Therefore the closed loop gain must be 1 (unity). In other words, the gain within the loop (provided by the amplifier) should exactly match the losses (caused by the feedback circuit) within the loop. In this ... |
The conditions for oscillation. |
Positive feedback must occur at a frequency where the voltage gain of the amplifier is equal to the losses (attenuation) occurring in the feedback path. For example if 1/30th of the output signal is fed back to be in phase with the input at a particular frequency, and the gain of the amplifier (without feedback) is 30 ... |
The oscillations should take place at one particular frequency. |
The amplitude of the oscillations should be constant. |
There are many different oscillator designs in use, each design achieving the above criteria in different ways. Some designs are particularly suited to producing certain wave shapes, or work best within a certain band of frequencies. Whatever design is used however, the way of achieving a signal of constant frequency a... |
Method 1 |
Make sure that positive feedback occurs only at one frequency, the required frequency of oscillation. This may be achieved by ensuring that only signals of the required frequency are fed back, or by ensuring the feedback signal is in the correct phase at only one frequency. |
Method 2 |
Make sure that sufficient amplification for oscillation can take place only at the required frequency, by using an amplifier that has an extremely narrow bandwidth, extending to the frequency of oscillation only. |
Method 3 |
Use amplifiers in "switch mode" to switch the output between two set voltage levels, together with some form of time delay to control the time at which the amplifiers switch on or off, thus controlling the periodic time of the signal produced. |
Fig. 1.1.2 The Need For Amplitude Stability |
Methods 1 and 2 are used extensively in sine wave oscillators, while method 3 is useful in square wave generators, sometimes called aperiodic (untuned) oscillators. Oscillators using method 3 often use more than one amplifier and timing circuit, and so are called multivibrators (more than one oscillator). |
Constant Amplitude |
As shown in Fig. 1.1.1 oscillators must have an amplifier, a positive feedback loop and some method of controlling the frequency of oscillation. In RF sine wave oscillators the frequency may be controlled by an LC tuned circuit, but as well as controlling the frequency of oscillation, there must also be some means, suc... |
Without this stabilisation the oscillations would either die away and stop (damped oscillation) or rapidly increase in amplitude until the amplifier produces severe distortion due to the transistors within the amplifier becoming "saturated" as shown in Fig. 1.1.2. To produce a constant amplitude output the gain of the ... |
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Elis Can't Hold On To Pair of Leads |
Jack Warhola image |
Jack Warhola image |
Fall to Bobcats 5-2 |
NEW HAVEN, Conn.Frankie DiChiara's two-goal night and a pair of one-goal leads early on were not enough to get the Yale men's hockey team a victory. No. 19 Quinnipiac erased the last deficit with four straight goals in a 5-2 win before a packed Ingalls Rink. |
The Bulldogs spent much of the night killing off penalties (8), which resulted in three Bobcats power-play tallies on a night full of big hits. Many of those hits were penalized, which meant that Yale goalie Patrick Spano was much busier than his 17 saves might indicate. |
It was also a night of few (42 combined) shots on goal. Quinnipiac got 10 of its shots with the advantage, while Yale put four on its four chances. |
DiChiara scored in two different periods, including Yale's first short-hander of the year, and now has nine goals this season. |
"I liked the way our guys competed, but I'm not happy with the result," said Keith Allain '80, Yale's Malcolm G. Chace Head Coach. "We competed harder than we did last night." |
The Bulldogs were the first to be fed, in the form of a DiChiara goal 4:22 into the game. The Eli senior was set up by linemate Joe Snively, who threaded the needle to put the puck on his stick in the high slot from behind the net. DiChiara gathered, cocked and released top shelf. |
"Joe [Snively] is so skilled with the puck," said DiChiara. "He is pretty crafty, and I was fortunate to be on the receiving end of that. It was an impressive pass." |
A major penalty called on Yale midway through the frame gave Quinnipiac the opportunity to more than erase the deficit, but the Eli special teams came up big in allowing just one tally. Spano made five saves and his teammates cleared the zone enough to send the game to intermission tied at 1-1. |
However, the Elis still had to kill off a penalty that went the last minute of the first and the opening segment of the second. It didn't get any easier after that kill. In the second minute of the period, the Blue took another five-minute major, but this kill had a different start and ending. |
Snively, applying pressure in the visitor's end on the kill, picked a pocket and was going in ahead of the defense when he got pulled off the puck and drew a raised zebra arm. He managed to shoot the puck but it landed behind the cage, where DiChiara grabbed it. Big No. 17 zipped around the net and sent a wrap-around s... |
The Bobcat penalty came off the board and the 4-on-4 went back to a QU advantage, which quickly turned into a 2-2 game. |
The visitors got an even-strength tally to grab their first lead at 14:22, and it stayed that way heading into the third. The second period ended just as it began, other than Yale being down a goal, with Quinnipiac on a power play that ran into the next period. |
The Bulldogs, who had to kill off seven minutes of penalty time in the first frame, had to erase five minutes in the second, and still managed to outshoot the Cats 9-7. |
Yale had some early, third-period opportunities to even things, especially on a power play. John Hayden barely missed an open left side of the net, and his teammates had other grade-A chances. It wasn't bad enough that none of those found the net, the Elis had to endure a Quinnipiac player kicking in a goal (video revi... |
The Bulldogs entered the weekend with a six-game unbeaten streak that included a weekend sweep of Brown… Rob O'Gara '16, a defenseman for the Boston and Providence Bruins this season, was on hand for tonight's game… Yale is on the road next week to play Cornell and Colgate… |
Cubic inches to quarts (liquid) (in³ to qt) Metric conversion calculator |
Welcome to our cubic inches to quarts (liquid) (in³ to qt) conversion calculator. You can enter a value in either the cubic inches or quarts (liquid) input fields. For an understanding of the conversion process, we include step by step and direct conversion formulas. If you'd like to perform a different conversion, jus... |
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1 in³ = 0.01731602 qt 1 qt = 57.75 in³ |
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Dozens in Greece, Bulgaria denounce Turkey & NATO in solidarity marches with Russia (VIDEOS) |
Turkey’s two neighbors and historical adversaries Greece and Bulgaria have witnessed sporadic protests denouncing Ankara’s remorseless in the shooting down of the Russian Su-24 plane, as well as NATO warmongering in general. |
Several dozen activists protested in Athens’ Syntagma square and marched to the Turkish embassy, where they staged a symbolic burning of American and Turkish flags. Additional police were deployed to guard the embassy as protesters voiced anger over the Sukhoi Su-24 jet downing by Ankara’s F-16 for allegedly entering T... |
This action of Turkey was totally unacceptable, a clear act of war, no unjustified action, an action which causes wider dangers in the area,” said Panagiotis Lafazanis, leader of fringe left-wing party Popular Unity. |
We want peace in the region, both in Greece and in Turkey, also in Kurdistan, in Syria and in Ukraine. [We want] peace and also the right to the peoples to determine their fate, without interventions from outside,” said Andreas Zafiris, representing the ‘Save Syria from NATO’ and ‘Save Donbass’ organizations. |
Marching further with a banner reading “Turkey and NATO are the same, when helping ISIS”, activists made a stop in front of the Greek Parliament, as well as at EU offices on Amalia Avenue. |
They ignore that the Russian airplane has dropped its bombs on the terrorists of the nearby Islamic State which threatens the whole world with terrorist attacks,” said Dr. Panagiotis Xanthopoulos, from the Panhellenic Union of Pontian Scientists. |
In the Bulgarian of capital Sofia, a crowd shared the same sentiment as in Greece. Activists from the opposition nationalist Ataka party rallied outside the Turkish embassy in solidarity with Russia over tensions with Ankara. |
One protester carried a banner bearing a picture of Russian President Vladimir Putin with the slogan “We have not forgotten, we will revenge,” apparently referencing to Russia's role in helping Bulgaria achieve independence from Turkey following the Russo-Turkish War (1877–1878). |
Banners reading “Friends of Russia and Orthodox world” and “Occupiers NATO and USA, out of Bulgaria!” were also seen among the crowd. |
During the protest Ataka party leader Volen Siderov praised the Russian operation in Syrian skies and accused the US of being incapable of dealing with Islamic State effectively. |
We are under a situation in which Russia is fighting against terrorism. And effectively. For two months, the Russian army has done everything that the Americans, French and German people and others couldn’t do for a year and a half,” Siderov stated. “And what does it mean? It means that Russia became a geopolitical pla... |
Monday, May 09, 2005 |
Religion: the New O. J. |
Something was nagging at me about America's current obsession with religion. Something familiar. |
OK, so this is what it's come to. We've got Wal-Churches, Focus on the Family, The Christian Coalition, Fox News, Karl Rove, Albert Mohler, James Dobson, Pat Robertson, Bill Frist, dozens of channels of TVangelists with shiny teeth and greasy hair, a dead pope, a pope just slightly this side of dead, and a president wh... |
Where have I had this feeling before? |
Let's see... in the 80s we had the Moral Majority, led by of dozens of self-anointed celebrity TVangelists, all of whom later got caught stealing or screwing or lying or embezzling or gold plating all kinds of silly shit in their palatial bathrooms. We had a president, Ronald Reagan, who acted immorally in almost every... |
And yet, the deja vu just isn't the same. |
As maddening and sad as Reagan was, with his dementia, his insulting trickle-themed economic programs, his insipid First Lady, his Iran-Contra, his Poindexter, his Ollie, his head-shaking self-righteousness, his threats to nuke the world, his corrupt cabinet, his ketchup-as-a-vegetable philosophical depth, and his see-... |
So where have I had this feeling before? This feeling that we're under a scratchy, woolen, 24/7 blanket of obsessive compulsion? That every act, no matter how large or small, no matter how mow-the-lawn tedious or boil-some-noodles mechanical, is somehow, some way, connected to God or Jesus or Satan or Osama or Dubya or... |
Christ, as an American news consumer, I think about religion more than the Pope. And I don't even believe in religion. |
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