Transistors
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A transistor is a âdeviceâ in which a high power current acts as a switch that can turn on and off the circulation of a lower power current. The later then may act as a switch in another transistor. To get this working you need to amplify the incoming low power current from the first transistor to make it a high power current that will pass through the second transistor is this correct?
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A transistor is a âdeviceâ in which a high power current acts as a switch that can turn on and off the circulation of a lower power current. The later then may act as a switch in another transistor. To get this working you need to amplify the incoming low power current from the first transistor to make it a high power current that will pass through the second transistor is this correct?
Calin Negru wrote:
a high power current acts as a switch that can turn on and off the circulation of a lower power current
Rather the other way around: A low power current can switch a higher power current on and off. Or, in analog transistors: Turn up or down the high power current proportionally to the controlling low power current. So the purpose of the transistor was to amplify the signal. In digital circuits, you really do not need this amplification. The output from the first transistor need only be strong enough to turn the second transistor on (i.e. opening it to let a signal through) or off. Under special circumstances, where the output of the first transistor is distributed to a whole row of second transistors, e.g. located on the row of plugin cards on a mainboard bus, the output signal must be strong enough to feed everyone of them. You don't see much of that any more: In the days of S100, ISA and MCA buses, you could plug 4-5-6-7 cards into a bus, side by side - the bus was like an AC power strip, delivering signals to a lot of recipients. You don't see much of that any more, partly because lots of what once required a large extension card now is provided on the CPU (or supporting 'chip set'), and partly because new bus standards have reduced the maximum 'fan out', to reduce the requirements for the bus electronics. Actually, lots of what we today refer to as 'bus' interconnects are really one-to-one signal lines. (For the pedantic ones: It still isn't wrong to call it a 'bus': (Omni)bus means no more than 'For everyone'. In the days when the COM and LPT ports were used for 'everything', they were '(omni)busses', linguistically speaking.) But talking about bus fanout and that sort of thing are special cases. Within a CPU, the current delivered from the output of a transistor is always enough to drive the input of the following transistor(s), even if there might be two or three of them receiving the same signal.
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Calin Negru wrote:
a high power current acts as a switch that can turn on and off the circulation of a lower power current
Rather the other way around: A low power current can switch a higher power current on and off. Or, in analog transistors: Turn up or down the high power current proportionally to the controlling low power current. So the purpose of the transistor was to amplify the signal. In digital circuits, you really do not need this amplification. The output from the first transistor need only be strong enough to turn the second transistor on (i.e. opening it to let a signal through) or off. Under special circumstances, where the output of the first transistor is distributed to a whole row of second transistors, e.g. located on the row of plugin cards on a mainboard bus, the output signal must be strong enough to feed everyone of them. You don't see much of that any more: In the days of S100, ISA and MCA buses, you could plug 4-5-6-7 cards into a bus, side by side - the bus was like an AC power strip, delivering signals to a lot of recipients. You don't see much of that any more, partly because lots of what once required a large extension card now is provided on the CPU (or supporting 'chip set'), and partly because new bus standards have reduced the maximum 'fan out', to reduce the requirements for the bus electronics. Actually, lots of what we today refer to as 'bus' interconnects are really one-to-one signal lines. (For the pedantic ones: It still isn't wrong to call it a 'bus': (Omni)bus means no more than 'For everyone'. In the days when the COM and LPT ports were used for 'everything', they were '(omni)busses', linguistically speaking.) But talking about bus fanout and that sort of thing are special cases. Within a CPU, the current delivered from the output of a transistor is always enough to drive the input of the following transistor(s), even if there might be two or three of them receiving the same signal.
trønderen wrote:
Or, in analog transistors:
I'm one of the pedantic ones. :-D A transistor is a transistor. There's no analog transistor and no digital transistor, it's a transistor.
The difficult we do right away... ...the impossible takes slightly longer.
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trønderen wrote:
Or, in analog transistors:
I'm one of the pedantic ones. :-D A transistor is a transistor. There's no analog transistor and no digital transistor, it's a transistor.
The difficult we do right away... ...the impossible takes slightly longer.
OK, you are certainly right about that. Also: Turning an ordinary light switch 'off' doesn't create an absolute insulation between the poles of the switch. The air gap just increases the resistance. A sufficiently high voltage may be able to cross that air gap. Certainly: That kind of voltage would also be able to do wonders to your PC and other semiconductor eqipment.
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Calin Negru wrote:
a high power current acts as a switch that can turn on and off the circulation of a lower power current
Rather the other way around: A low power current can switch a higher power current on and off. Or, in analog transistors: Turn up or down the high power current proportionally to the controlling low power current. So the purpose of the transistor was to amplify the signal. In digital circuits, you really do not need this amplification. The output from the first transistor need only be strong enough to turn the second transistor on (i.e. opening it to let a signal through) or off. Under special circumstances, where the output of the first transistor is distributed to a whole row of second transistors, e.g. located on the row of plugin cards on a mainboard bus, the output signal must be strong enough to feed everyone of them. You don't see much of that any more: In the days of S100, ISA and MCA buses, you could plug 4-5-6-7 cards into a bus, side by side - the bus was like an AC power strip, delivering signals to a lot of recipients. You don't see much of that any more, partly because lots of what once required a large extension card now is provided on the CPU (or supporting 'chip set'), and partly because new bus standards have reduced the maximum 'fan out', to reduce the requirements for the bus electronics. Actually, lots of what we today refer to as 'bus' interconnects are really one-to-one signal lines. (For the pedantic ones: It still isn't wrong to call it a 'bus': (Omni)bus means no more than 'For everyone'. In the days when the COM and LPT ports were used for 'everything', they were '(omni)busses', linguistically speaking.) But talking about bus fanout and that sort of thing are special cases. Within a CPU, the current delivered from the output of a transistor is always enough to drive the input of the following transistor(s), even if there might be two or three of them receiving the same signal.
Thank you for your answer > Rather the other way around In that case doesnât the output power of the first transistor need to be reduced? To create Boolean logic you need low power to act as a switch on the second transistor
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OK, you are certainly right about that. Also: Turning an ordinary light switch 'off' doesn't create an absolute insulation between the poles of the switch. The air gap just increases the resistance. A sufficiently high voltage may be able to cross that air gap. Certainly: That kind of voltage would also be able to do wonders to your PC and other semiconductor eqipment.
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A transistor is a âdeviceâ in which a high power current acts as a switch that can turn on and off the circulation of a lower power current. The later then may act as a switch in another transistor. To get this working you need to amplify the incoming low power current from the first transistor to make it a high power current that will pass through the second transistor is this correct?
The simplest transistor to understand is the MOSFET used in most computer logic circuits. The name describes the construction and how it works đ Metal-Oxide-Semiconductor is a thin aluminium on a thinner glass layer on a doped silicon surface. The doping impurities change the silicon's behaviour. The FET part of the name is Field Effect Transistor. When a voltage is applied to the thin metal layer (gate) the charge acts across the insulating glass layer to pull carriers to the surface of the silicon, making a greatly more conductive channel for current at the surface. A very small amount of power to charge the gate can control much larger currents in the underlying semiconductor.
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Thank you for your answer > Rather the other way around In that case doesnât the output power of the first transistor need to be reduced? To create Boolean logic you need low power to act as a switch on the second transistor
Digital transistors are not built for amplification. Essentially, the signal being controlled is at the same level as the controlling one. The control consists of either let the controlled signal through, or to stop it. (Sort of like the main valve to turn on/off the water supply to your house: It is either open or closed, not intended to be in any intermediate position.) Like a water flow: If you open a valve completely, you won't have an infinite water flow, only as much as the source will supply. Same with transistors: A fully open transistor lets through whatever wants to get through, but in a digital circuit, that is not much more than the controlling signal. Both the controlling and the controlled signal are low power. In a modern CPU, such as an x64 CPU, that is really low power! I willingly admit that I do not know how low, but would be curious to know! Even if could have gotten access to the transistor (which is completely impossible inside the CPU) my multimeter would not be able to measure it. Not by several orders of magnitude.
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The simplest transistor to understand is the MOSFET used in most computer logic circuits. The name describes the construction and how it works đ Metal-Oxide-Semiconductor is a thin aluminium on a thinner glass layer on a doped silicon surface. The doping impurities change the silicon's behaviour. The FET part of the name is Field Effect Transistor. When a voltage is applied to the thin metal layer (gate) the charge acts across the insulating glass layer to pull carriers to the surface of the silicon, making a greatly more conductive channel for current at the surface. A very small amount of power to charge the gate can control much larger currents in the underlying semiconductor.
You can also make a transistor from a crystal and two needles :-) I guess that even software people have seen the classical transistor symbol used in circuit diagrams: A circle enclosing two slanted lines (one with an arrowhead), one from each side onto a bar, and a third line down from the bar; that is the control signal, steering how much current it let through from one needle to the other. The symbol is is a stylized drawing of the crystal and the two arrows. (For FETs the symbol is slightly modified; the lines are not slanted.) I have been with semiconductors for so long that I have been thinking of crystal transistors as something they used two generations ago. So I was surprised to discover that you still can buy them, in a lot of varieties; they are often preferred in certain high frequency radio application. These are individual transistor components, usually in a sealed glass capsule. You wouldn't build a computer from them :-)
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You can also make a transistor from a crystal and two needles :-) I guess that even software people have seen the classical transistor symbol used in circuit diagrams: A circle enclosing two slanted lines (one with an arrowhead), one from each side onto a bar, and a third line down from the bar; that is the control signal, steering how much current it let through from one needle to the other. The symbol is is a stylized drawing of the crystal and the two arrows. (For FETs the symbol is slightly modified; the lines are not slanted.) I have been with semiconductors for so long that I have been thinking of crystal transistors as something they used two generations ago. So I was surprised to discover that you still can buy them, in a lot of varieties; they are often preferred in certain high frequency radio application. These are individual transistor components, usually in a sealed glass capsule. You wouldn't build a computer from them :-)
Thanks
