how to measure characteristics of SN74HC74????

[saliva31]

Please I have to do the test measurement for the item on this data sheet, but i have to understanding the characteristics of this item:

1. Static power supply current
2. Output voltage
3. Clock frequency
4.Transmission delay time
5.rise time / fall time

anyone who can share the solution or option to get the source of this information please help me to understanding this item, before i can do the measurement test method. this planning method for my study to the better understanding and i have to apply this item to do the test method to the ic (SN74HC74) and i want to know how can i measure this item using Orcad Spice software?? can or cannot??

 

[Papabravo]

I'm not sure what you are trying to do. If you want to measure the characteristics of a real device then OrCad will be no help to you. I'm not sure that a SPICE simulation can accurately give you what you are looking for. As you know in a CMOS chip there is a quiescent current consumption, and there is a current consumption which depends on frequency and the square of the supply voltage.

When it comes to logic circuits, many SPICE simulators have a general purpose behavioral model where you get to specify things like rise time and fall time. Trying to get a SPICE package to match the family characteristics of a logic chip is no task for neophytes. Sorry chum, but I think you are outta luck.

 

[saliva31]

i have been given a task by my instructor to make a logic IC Testing Plan for SN74HC74, I just have a orcad simulation, i am refer the datasheet from texas Inst. the problem is How to measure this item, can we do a manually (means by using truth table or give clock signal to see the output follow by the item i have mention), or using Orcad simulation? So can you sharing with me any suggestion or opinion?

 

[Papabravo]

I already gave you my suggestions and opinions. I'll defer to someone else who thinks there is a way to accomplish this task with the given constraints. I don't see how you can use a piece of simulation software to test a piece of hardware. Like I said before you have to be resonably astute to transform a behavioral model into something that matches a real piece of silicon. I must be missing something.

 

[saliva31]

Rise Time, Fall Time

In the SN74HC74, the rise time and fall time can be measured in the circuit configuration that we design, but i have to know how to read the table in Control of input terminals (truth table)

what is the means by fixed on the table??

any explanation of this table

 

[Papabravo]

H means that the input is at a "High" Logic level
L means that the input is at a "Low" logic level

fixed means that it does not change.

H/L means a high to low transition

In a 74HCxx part if Vcc is +5Volts then the threshold for logic levels should be close to Vcc/2 = 2.5 Volts. That means that any level greater than 2.5 volts is considered a high and any level less than 2.5 volts is considered a low.

In most SPICE packages rise and fall times are behaioral parameters. That means you set the values to whatever you want them to be. They are not, repeat NOT, the result of simulating a model of the 74HC74 built from individual transistors.

This is why your post is so confusing. You seem to think that a SPICE simulator is doing things which it does not do. I don't know where these notions come from.

 

[ericgibbs]

hi,
Do a Google search for SZZA036B

Its a Texas Instruments document pdf that explains how to read datasheets.

Its about 900K.

 

[Hero999]

Just look at the datasheet, you can't measure any characteristics using SPICE because it isn't real, it's a simulation.

 

[Roff]

I think we have a language barrier here. I suspect his task is to measure the characteristics he listed, not of an actual IC, but of the spice model. The techniques could later be used, possibly with some modifications, on real hardware.

 

[Papabravo]

That is a plausible hypothesis except for one small detail. A SPICE simulator is unlikely to have a specific model for a 74HC74. What it will have is a behavioral model for a D Flip-Flop. You then enter parameters so that it behaves like the part you are interested in.

What we have here is a kind of chicken and egg problem. You can't simulate the parts without enteing the parameters, and you can't enter the parameters without understanding the datasheet, and you can't get the simulation to match the datasheet without a pretty deep understanding of the real part and the simulation process.

This is really not the student's fault, it is the boneheaded sadist of an instructor who is too lazy to teach. A pox on all the lazy instructors in the world. If he was doing his job, his students would not have to come to us with their hats in their hands asking for help on rediculous assignments.

 

[Roff]

That is a plausible hypothesis except for one small detail. A SPICE simulator is unlikely to have a specific model for a 74HC74. What it will have is a behavioral model for a D Flip-Flop. You then enter parameters so that it behaves like the part you are interested in.

What we have here is a kind of chicken and egg problem. You can't simulate the parts without enteing the parameters, and you can't enter the parameters without understanding the datasheet, and you can't get the simulation to match the datasheet without a pretty deep understanding of the real part and the simulation process.

This is really not the student's fault, it is the boneheaded sadist of an instructor who is too lazy to teach. A pox on all the lazy instructors in the world. If he was doing his job, his students would not have to come to us with their hats in their hands asking for help on rediculous assignments.

Here is the 74HC74 model that I use. I haven't checked its accuracy, but you could measure the parameters our OP specified in LTspice. A similar model may not be available for Orcad.

* D-filp-flop with asynchronous set and reset
* CP->Q Tpd 47n/17n/14n
* R/S->Q Tpd 52n/19n/15n
* CP/R/S Tw 19n/7n/6n
* D->CP Ts 6n/2n/2n 
* D->CP Th -6n/-2n/-2n
* R,S Trem 3n/1n/1n
.SUBCKT 74HC74  S C D R Q QN  VCC VGND  vcc1={vcc} speed1={speed} tripdt1={tripdt}
.param td1=1e-9*(17-5-3-3)*4.0/({vcc1}-0.5)*{speed1}
.param td2=1e-9*(19-5-3-3)*4.0/({vcc1}-0.5)*{speed1}
.param td3=1e-9*(17+2-5-3-3)*4.0/({vcc1}-0.5)*{speed1}
.param td4=1e-9*(5)*4.0/({vcc1}-0.5)*{speed1}
*
XIN1  S Si  VCC VGND  74HC_IN_1  vcc2={vcc1}  speed2={speed1}  tripdt2={tripdt1} 
XIN2  C Ci  VCC VGND  74HC_IN_1  vcc2={vcc1}  speed2={speed1}  tripdt2={tripdt1} 
XIN3  D Di  VCC VGND  74HC_IN_1  vcc2={vcc1}  speed2={speed1}  tripdt2={tripdt1} 
XIN4  R Ri  VCC VGND  74HC_IN_1  vcc2={vcc1}  speed2={speed1}  tripdt2={tripdt1} 
*
ACDEL  Ci 0 0  0  0   0   Cp 0  BUF  tripdt={tripdt1}  td={td1} 
ADDEL  Di 0 0  0  0   0   Dp 0  BUF  tripdt={tripdt1}  td={td3} 
ARINV  Ri 0 0  0  0   Rn  0  0  BUF  tripdt={tripdt1}  td={td2}
ASINV  Si 0 0  0  0   Sn  0  0  BUF  tripdt={tripdt1}  td={td2}
A1     Di 0 Cp Sn Rn  QNi Qi 0  DFLOP  tripdt={tripdt1} td={td4}
*
XOUT1  Qi  Q   VCC VGND  74HC_OUT_1X  vcc2={vcc1} speed2={speed1}  tripdt2={tripdt1}
XOUT2  QNi QN  VCC VGND  74HC_OUT_1X  vcc2={vcc1} speed2={speed1}  tripdt2={tripdt1}
.ends
*

There is an entire library (74HC.lib) on the **broken link removed**. There is also a 74HCT library, a CD4000 library, and many other useful models and subcircuits.

 

[saliva31]

thanx for all of your opinion, i will apply and understand to this characteristics,and yes we cannot using spice to to all of this items....

 

[Papabravo]

Yes, what you have is parameterized behavioral model built on top of the DFLOP primitive. The D-FF is not being simulated at the transistor level. A kind and brilliant soul like Helmut or Mike actually filled in the details and packaged it up. Do you know the specific details of the DFLOP primitive? All those other parameters you have to specify. As you correctly point out such a facility may or may not be present in OrCad.

LTSPICE is a great package and the guys who support it are some of the brightest stars I know of.