In today's highly integrated chips, most of them are CMOS devices

Today, chips are highly integrated , Most of them are CMOS device , and TTL Devices are rarely produced , Why are chips generally CMOS What about ？ also TTL and CMOS What does level say ？ After reading this article, you will know .

If you only look at the appearance of a chip , It's impossible to distinguish TTL perhaps CMOS Of , Because they are classified according to the chip manufacturing process , The essential difference is ,CMOS Internally integrated is MOS tube , and TLL Internally integrated is a triode .

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RTL This circuit is composed of resistors and triodes , This is a RTL NAND gate circuit , It can realize such logic , Only when two tertiary tubes are connected at the same time , His output is zero , Otherwise, his output is one , however RTL The circuit is slow and unstable , A few years later , Texas Instruments TTL Logic circuits are the latecomers .

TTL Its core is composed of triode and triode , This is a TTL NAND gate , Its function is the same as that mentioned above RTL equally , But more stable , The frequency is also higher ,TTL Circuit input and output characteristics , When T5 Conduction T4 At the deadline ,Y The output is low level , Voltage is T5 Of CE The saturation pressure drop between stages is about 0.3 v , When T5 end T4 Conduction time , At this time, the output voltage is about 3.6 v .

What then? TTL It is generally believed that the high level of the output is greater than 2.4 Volt instead of 3.6 Vomit ？ This is because TTL There are many kinds of circuits , At this time, it is necessary to choose the one with the lowest output high level , Like the barrel effect , Why? TDL The input high level of should be greater than 2.0 Vomit ？ When both inputs are greater than 2.0 When you fall , These three transistors can be completely turned on , It can output the desired low level .

Say again about 0.8 Low level of volts , If there is an input less than 0.8 v ,E The point voltage will be pulled down , here T5 end ,T4 Conduction , At this point, the output 3.6 High voltage level , In a steady state ,T4 and T5 There can only be one conduction , These two diodes play an avant-garde role , It can suppress the negative polarity pulse at the input , It can also limit the current , To protect .

TTL The advantage of logic circuit is fast , But there is a drawback that makes it impossible to integrate on a large scale , That is, the static current loss of the triode is very large , In view of this , People have invented that the speed is relatively slow , But static current is zero CMOS logical circuit , Complementary because N type MOS and P type MOS At the same time, it appears in the circuit .

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This is a CMOS NAND gate , Its function is the same as that mentioned above TTL And not the door is exactly the same , You see, the semiconductor devices in it are MOS tube , because MOS The static power consumption of the tube is almost zero , So it can be integrated on a large scale in the chip , When the input is also high .

MOS The conduction of the tube is like this , At this time, the output level is close to 0V, As long as one input is low ,Y You can output high point level , because T1 The conduction impedance of is very low , We can think of the output level as 5V, This is it. CMOS Full output characteristics of .

This is a CMOS Input and output characteristics of the circuit , Then there is another question , The MCU we use is CMOS device , And what communicates with computers is TDL turn USB,CMOS The device can directly drive TTL Do you ？ Of course ,CMOS The high level of the output is close to 5V Your battery is close to 0V, and TTL The input high level of is greater than 2V, The low level is less than 0.8 v , Look at it this way CMOS It can be driven directly TTL Of .

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