[SOLVED] Transistors and FET switching times and duty cycles

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PrescottDan

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What are some common voltages that turns on a transistor? 1.7 vdc?
What are some common voltages that turns on a CMOS FET?

A FET switching speed is faster then a transistors switching speed?

What makes a FET have such a faster switching speed? why are transistors slow at switching speed?

FETS can be turned on by High frequency's, but have a problem getting turned on my lower frequency's?

How do you change a transistor and FETS switching duty cycle? the turn on speed can be fast but the turn off can be slow

When using an Oscope, how can you measure a transistor and FETS switching speed and switching duty cycle?

Channel#1 on input of a transistor or FET
Channel#2 on the output of a transistor or FET

This will be in nanoseconds, can an Oscope time base has a setting to do this? or only a logic analyzer have to be used?

Have to use a Storage Oscope with the time base setting at which timing setting speed?

TTL logic components like TTL gates don't like high frequencies logic waveforms? CMOS Logic components is better at high frequency logic signals and waveforms?

TTL logic components have a slow response time and a slow switching time compared to CMOS logic components
 

"I have answered three questions, and that is enough!",
said the Father. "Don't give yourself airs. Do you think I
can listen all day to such stuff? Be off, or I'll kick you
down stairs".

- "Father William", Lewis Carroll

Now as to your final question, this was not always the
case. In the early '80s CMOS was the low power dog
and anything that had to be fast was Schottky TTL
or if it had to be real fast, ECL. Times change, and
yesterday's prom king is tomorrow's assistant manager.
 

How can the base-emitter voltage of a transistor be as high as 1.7V when in most low current transistors it is only 0.7V?
Easy. Blast a very high base current into a power transistor like a 2N3055. Its datasheet shows that its typical base-emitter voltage is 1.7V when its base current is 900mA.

The datasheet for a Cmos logic IC shows the input voltage range that turns it on.

The datasheets also show switching speeds.
The datasheet for an ordinary slow CD4xxx Cmos IC has a very low 4mA maximum output current.
The datasheet for a 74HCxxx high speed Cmos logic IC has a fairly high 48mA maximum output current.
Don't you think that the much higher current can charge and discharge stray capacitances much faster??

Why don't you ever look at datasheets??
 

Why don't you ever look at datasheets??
Click to expand...

Is it a "standardization" that TTL is slower in switching speeds compared to CMOS? is this true or false?

Or does it depend on each TTL/CMOS IC chips datasheet

Is it true that it's more difficult to sync TTL logic signals compared to syncing CMOS logic signals?

The Switching Duty cycle (the turn on and off switching times) of TTL IC chips have a different switching duty cycle compared to CMOS chips switching duty cycle, the turn on and off switching times?

Having different switching on and off times makes it difficult to "sync" the signals?

- - - Updated - - -

Syncing TTL IC chips or CMOS chips to what?
1.) A clock?
2.) A timer?
3.) An Oscillator?
4.) What else can you sync TTL Or CMOS chips to?

- - - Updated - - -

How do you measure a Transistor Reverse Recovery Time using an Oscope?

Channel#1 on the input of the transistor
Channel#2 on the output of the transistor?

What do you use as an input generator? a ramp or step generator? or square waveform?
 

PrescottDan said:
Is it a "standardization" that TTL is slower in switching speeds compared to CMOS? is this true or false?
Or does it depend on each TTL/CMOS IC chips datasheet
Click to expand...
There are about 4 different families of TTL and there is CD4xxx ordinary Cmos and 74HCxxx high speed Cmos. You need to learn about all these families.

Is it true that it's more difficult to sync TTL logic signals compared to syncing CMOS logic signals?
Click to expand...
Syncing is simple with any logic family.

The Switching Duty cycle (the turn on and off switching times) of TTL IC chips have a different switching duty cycle compared to CMOS chips switching duty cycle, the turn on and off switching times?
Click to expand...
Duty cycle is completely different from turn on and turn off switching times. Duty cycle is the ratio of high and low durations.
The input duty cycle determines the output duty cycle, not whether the chip is TTL or Cmos, but logic might invert the duty cycle.

Having different switching on and off times makes it difficult to "sync" the signals?
Click to expand...
No. Syncing is simple and has nothing to do with switching on and off times.
Some counters are triggered with a high edge and other counters are triggered with a low edge. The datasheet tells you the minimum risetime or falltime of the triggering edge. A Schmitt trigger clock input is triggered with a certain voltage, not an edge, then the risetime or fall time does not matter. The datasheet tells you all about it.

Syncing TTL IC chips or CMOS chips to what?
1.) A clock?
2.) A timer?
3.) An Oscillator?
4.) What else can you sync TTL Or CMOS chips to?
Click to expand...
Old analog TVs used sync circuits, not logic ICs. An FM stereo decoder is synced with the 19kHz broadcast pilot tone.
Why are you asking about syncing when you have no idea about what a circuit needs to sync with???

How do you measure a Transistor Reverse Recovery Time using an Oscope?
Click to expand...
Why would anybody need to measure it when it is listed on the datasheet??
 

Duty cycle is completely different from turn on and turn off switching times.
Click to expand...

Since it's not called a duty cycle, what is the switching turn on and turn off times called? is the turn on called Mark and the turn off called space? mark and space ratio?

Old analog TVs used sync circuits, not logic ICs.
Click to expand...

What are these TV sync circuits called? since they didn't use logic IC chips what did they use to create a sync circuit?

Why would anybody need to measure it when it is listed on the datasheet??
Click to expand...

To either speed up or slow down the Reverse Recovery time of a transistor

Would a tech up a step generator as the input? to measure a transistors switching on/off times and reverse recovery time?
 

PrescottDan said:
Since it's not called a duty cycle, what is the switching turn on and turn off times called? is the turn on called Mark and the turn off called space? mark and space ratio?
Click to expand...
Switching times are a risetime and a falltime.
Mark and space might be used to describe the duty cycle of old Morse Code communication.

What are these TV sync circuits called? since they didn't use logic IC chips what did they use to create a sync circuit?
Click to expand...
Duh! They were called "sync circuits". The first ones used vacuum tubes then later they used transistors. My TV made in 1971 used an IC called a "jungle" IC that was made to be used in a TV.

Would a tech up a step generator as the input? to measure a transistors switching on/off times and reverse recovery time?
Click to expand...
I do not know why a tech would measure switching on/off times and reverse recovery time. Oh, maybe because the tech never learned how to read (the datasheets), or because he is guessing at using a substitute transistor without looking at its datasheet.
 

  • FETs have voltage controlled resistance with a threshold effect determined by geometry and fab
  • this has improved over the decades in Enhancement mode MOSFETs standardized from 4.5V to 2.5 ... to 400mV for LVC2 logic level drive.
  • High Threshold CMOS such as HCMOS series has a wide Vdd range and threshold is always Vdd/2 {±30%}.
  • TTL input threshold is always 2"PN" drops or 1.3V, regardless of 74xx, 74ALS etc.
  • Specs always define rise/fall as Transition time and Propagation delay tTHL, tTLH and tpHL,tpLH
  • old TV's used Injection Locked Loop (ILL) not PLL. Capture range depended on initial offset error. We control de horizontal!
  • Anyone with reading skills can fetch these answers on their own
  • BTW, DigiKey lists over 100 Logic Families for a logic inverter, not 10.
 

Duh! They were called "sync circuits".
Click to expand...

Yes I know that, but is it an Oscillator , a timer or clock?

there is two sync circuits, the horizontal sync circuit is at what frequency? the vertical sync circuit is at what frequency?

Why do they need to sync the video signals?

reverse recovery time.
Click to expand...

Is the Reverse Recovering time, the transistors turn off time?

"sync circuits"
Click to expand...

An Oscope has a Sync circuit, for the display

When a circuit uses a PLL, a timer or clock, is this considered syncing? or is just using an Oscillator circuit only considered the as a sync source?

If a circuit syncs it's logic signals to a timer or a clock or a PLL is this considered syncing? or only for oscillators circuits is this considered to sync too?

When measuring a circuit like a TV circuits if the signals are in- sync

O-scope channel#1 is the sync circuit" oscillator
O-scope channel#2 is horizontal signal
O-scope channel#3 is the vertical signal
O-scope channel#4 is the video signals

How do you if they are all in sync? set the Oscope to normal trigger mode? or you have to use the external trigger?
 

PrescottDan said:
Yes I know that, but is it an Oscillator , a timer or clock?

there is two sync circuits, the horizontal sync circuit is at what frequency? the vertical sync circuit is at what frequency?

Why do they need to sync the video signals?
Click to expand...
Why don't you learn about old fashioned analog TV circuits yourself?

Is the Reverse Recovering time, the transistors turn off time?
Click to expand...
Please look in Google.

An Oscope has a Sync circuit, for the display
Click to expand...
Of course.

When a circuit uses a PLL, a timer or clock, is this considered syncing?
Click to expand...
Usually not. The "P" is for phase, not frequency.

or is just using an Oscillator circuit only considered the as a sync source?
Click to expand...
Yes, usually an oscillator is the source you want to sync to.

If a circuit syncs it's logic signals to a timer or a clock or a PLL is this considered syncing? or only for oscillators circuits is this considered to sync too?
Click to expand...
A timer, clock and PLL have an oscillation that you can sync to if you need to.

When measuring a circuit like a TV circuits if the signals are in- sync

O-scope channel#1 is the sync circuit" oscillator
O-scope channel#2 is horizontal signal
O-scope channel#3 is the vertical signal
O-scope channel#4 is the video signals
Click to expand...
It seems that you know nothing about old analog TV signals and know nothing about an oscilloscope.

How do you if they are all in sync? set the Oscope to normal trigger mode? or you have to use the external trigger?
Click to expand...
An oscilloscope usually has a TV sync circuit inside. Don't you know that the sync signals are mixed with the video and color signals?
 

An oscilloscope usually has a TV sync circuit inside. Don't you know that the sync signals are mixed with the video and color signals?
Click to expand...

Yes you can use the Oscope Trigger TV mode or you can use Oscope channel#1 and probe the sync circuit

A timer, clock and PLL have an oscillation that you can sync to if you need to.
Click to expand...

Are logic circuits synced like this using a clock, a timer, or PLL or only to an oscillator sync circuit?

Don't you know that the sync signals are mixed with the video and color signals?
Click to expand...

yes I know, so which sync do you use , the horizontal sync or vertical sync for which color signals and video signals?

How do you measure if the color and video signals are in SYNC and not offset or out of sync? use a storage Oscope?
 

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