科技英语论文.doc

Title: Timer circuits
Faculty: Electrical engineering
Major: Electronic information science and technology
Class:0309411
Student Name:钱进红
Student Number:030941103
Summary:The circuit is generally an overkill in many respects, but when initially designed I did not know what range of frequencies might eventually be required. So I added the extra transistor here and there because it improved potential performance. As it happens, much lesser stability and range would have been perfectly satisfactory.
The connection marked 'gang' was provided so that two such oscillators could be connected together. The faster oscillator will dominate and both will work in synchronism.
Much of the circuit is in fact parator made with discrete transistors. Indeed, there is no good reason why parator should not be used. However with the darlington arrangement shown, base current is quite tiny. For even smaller base current, the long-tailed pair could be exchanged for a pair of JFETs. Modern silicon transistors can work down to a new nanoamps, so the charge current can be quite tiny. How about increasing C1 and making an oscillator which pulses once a week?
Key words: oscillators, comparator, base current
Multivibrators: an old, well known and boring subject. No - not at all: there are lots of different ways of looking a them and they are not at all what they may seem.
What exactly is a multivibrator? I suppose one definition would be 'a circuit which has several states'. This will do for now, it's quite loose so leaves plenty to the imagination. Conventional multivibrators have only two stages e in three flavours: astable (where neither state is stable and the circuit oscillates between the two states); monostable (where one state is stable, the other transient). And bistable, where the circuit can be flipped from state one to state two. The fact that it can be 'flopped' back again leads to another term 'flip-flop' - but you can call an astable an astable flip-flop! Then you