What are the differences between a power supply for a TTL circuit compared to a CMOS circuit

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Calton57

Joined May 4, 2015
33
What are the differences between a power supply for a logic TTL circuit compared to a logic CMOS circuit?
A power supply for a logic TTL circuit has series pass transistors but a power supply for a logic CMOS circuit doesn't use series pass transistors.

The series pass transistors stabilizes the fluctuations and stablizes the +5 volt to be + or - 0.25 volts?

CMOS power supplies don't have series pass transistors

CMOS power supplies have a high noise immunity?

The Noise Immunity is higher on logic CMOS circuit boards compared to TTL logic boards?

In CMOS logic there is no current flowing , only leakage current flow?
 

crutschow

Joined Mar 14, 2008
31,091
CMOS circuits generally take less power, which starts as leakage current when in a static state and increases with operating frequency. It may approach the value of TTL logic at high operating frequencies.
TTL circuits draw a significant static current which increases only a small amount with operating frequency.

Series pass transistors can be used for any regulated linear supply.

CMOS circuits (particularly the old CD4000 series) have a wider operating voltage range than TTL logic so may not require a regulated voltage.

CMOS circuits have a voltage swing equal to the supply voltage, so have a higher noise immunity than TTL when operating at 5V or above.
 

Thread Starter

Calton57

Joined May 4, 2015
33
What is causing the high noise immunity? is it the print circuit board traces and lay out or the power supply?

What is causing leakage current in CMOS chips? TTL chips don't have leakage current?

The operating frequency is determined by the clock frequency?
 

dl324

Joined Mar 30, 2015
15,406
What is causing the high noise immunity? is it the print circuit board traces and lay out or the power supply?
The threshold voltages of the P and N devices.
What is causing leakage current in CMOS chips?
Non-ideal characteristics of MOSFETs.
The operating frequency is determined by the clock frequency?
In "simple" logic. Microprocessors have PLLs for frequency generation. Doublers, triplers, etc are possible using simpler means.

Max operating frequency is largely determined by propagation delays.
 

Thread Starter

Calton57

Joined May 4, 2015
33
where is the operating frequency coming from in TTL circuits and CMOS circuits? i thought the operating frequency was from the clock circuit

The threshold voltages of the P and N devices.
The Threshold voltages cause noise immunity? i don't get how a threshold voltage would cause noise in a circuit
 

Papabravo

Joined Feb 24, 2006
19,551
A little homework for you.
What is the threshold voltage of a CMOS gate with Vcc = +5VDC and Vxx = GND?
What is the input low threshold for a TTL gate?
What is the input high voltage for a TTL gate?
What is the difference between the input high and the input low thresholds?
Is it greater than or less than the CMOS threshold?
I think you just answered your own question. Isn't that a wonderful feeling?
 

crutschow

Joined Mar 14, 2008
31,091
where is the operating frequency coming from in TTL circuits and CMOS circuits? i thought the operating frequency was from the clock circuit.
The operating frequency is determined by whatever is generating the signals.
In most circuits there is a clock that determines the highest operating frequency.

The Threshold voltages cause noise immunity? i don't get how a threshold voltage would cause noise in a circuit
You are confused with your terms.
Nose immunity is immunity to noise generated elsewhere that appears at the logic inputs.
It has nothing to do with the cause of noise.
 

Thread Starter

Calton57

Joined May 4, 2015
33
The operating frequency is determined by whatever is generating the signals.
In most circuits there is a clock that determines the highest operating frequency.

You are confused with your terms.
Nose immunity is immunity to noise generated elsewhere that appears at the logic inputs.
It has nothing to do with the cause of noise.
What else can be generating the signals besides a clock circuit

The clock circuit determines the switching speed of each IC logic chip

What is causing noise immunity on the logic's inputs? the printed circuit board traces or layout or power supply or components?
 

dl324

Joined Mar 30, 2015
15,406
The IC chips input impedance and output impedance is one of the causes of noise immunity
Not even close.

This is from a Fairchild application note:
"noise immunity is defined as the maximum noise voltage which can appear on the input without switching an inverter from one state to another"

It is primarily a function of the input threshold voltages.

This has been stated multiple times. Are there some phrases/words that need further explanation?
 

Thread Starter

Calton57

Joined May 4, 2015
33
dl324
"noise immunity is defined as the maximum noise voltage which can appear on the input without switching an inverter from one state to another"
Yes I under this part

What I don't understand, is where is the noise coming from that is being applied to the input of the IC chip?

dl324
It is primarily a function of the input threshold voltages.
Yes I know this because All these technologies has different maximum noise immunity levels or thresholds

RTL
DTL
TTL
CMOS
ECL
EECL
HTL
PMOS
NMOS
 

dl324

Joined Mar 30, 2015
15,406
So what are the main differences between a power supply for a TTL logic circuit VS a power supply for a CMOS circuit?
As previously mentioned, TTL supplies would typically need to provide more current. Additionally, CMOS has a wider range of operating voltages.
 
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