My instructor mentioned that a NAND gate can be wired as an amp. How is this possible?

 

Is your instructor talking about TTL or CMOS logic gates?

Ken

 

I'm sorry, he is talking about CMOS logic.

 

Yup!, (s)he's right: http://www.fairchildsemi.com/an/AN/AN-88.pdf

Ken

 

Thanks for the reply. I am having trouble understanding how. i can create a NAND equivalent inverter but the amps in the link you posted are for AC. The application I would use it for is DC.

 

Here is another discussion: http://www.electronics-related.com/usenet/design/show/2285-1.php
In reality they are not very good opamps. Why do you want to use one instead of a real opamp? What are you designing?

Ken

 

We are designing a circuit or (modifying one) from another we had that blinked LEDs. We are using the same parts basically. They are 4093 (I think), some resistors, two 3904, two LEDs, piezo buzzer.

The buzzer is going to be wired as a transducer. When you whistle into the buzzer the LEDs will light.

 

The CD4093 has NAND gates with Schmitt-trigger inputs that cannot be used as an amplifier.

A Cmos "amplifier" is very non-linear when its output voltage is close to ground and close to the supply voltage. Therefore it is used as an AC amplifier with its output almost always near half the supply and far away from ground and the supply voltage.

 

You posted before I could correct it. I'm using a 4011. i guess my problem is the AC part. This circuit is DC.

 

A two-input NAND gate is more symmetrical as an amplifier when only one input is part of the amplifier and the other input is connected to the positive supply voltage.
When both inputs are connected together then the symmetry is poor.

But all the Cmos amplifiers I have made and have seen were made from inverters, not Buffered B-suffix gates so an oscillator made from a gate might not work properly.

 

Correction:
I made an oscilloscope callibrator 32 years ago and inside is a CD4011B IC.
It works perfectly.

But it is a square-wave oscillator, not a linear amplifier.

 

I figured it out. Thanks for your help. I am only having trouble getting enough gain to actually light the LEDs. I will try tying one input to VCC. Thanks.

 

We can't help you since you did not post your schematic.

 

Here it is:

 

Your NAND gate is not powered so it will not do anything.
Your circuit has a voltage gain of almost 10,000 if it is fed from a very low impedance source. But if the input is an electret mic powered from a 10k resistor then the 1k input impedance of this amplifier is loading down the output from the mic so the total gain is reduced to a few thousand which should be plenty if you talk close to the mic.

But like I said earlier, a Cmos amplifier is usually made with a single stage inverter, not a multi-stage buffered gate so it might not work.

 

MultiSIM doesn't show the power pins. I have nine volts on it.

You may be right. i am getting the 10,000 gain, but it won't light the LED. Also I can't keep the waveform in the circuit consistantly.

e.g. If I measure the piezo input and I have a wave form I should see it at the inputs and then w/ gain at the out put. This is not always the case. Sometimes it is abnormal shape. Sometimes it is a green blob (like there is a bunch of noise on the scope) It is hard to describe and I have no way to show you.

More than likely it's just not possible to do what I want with what I have.

 

Your very high gain "amplifier" is probably oscillating at a high frequency. Oscillation looks like a "geen blob" or as noise on a 'scope. The usual Cmos amplifier is a single-stage inverter from a CD4069 or 74C04 IC.

The supply voltage affects the gain of a Cmos amplifier made from an inverter. See my attachment.

What is the piezo for? Usually a piezo is a transducer that is used as a low level, high audio frequency beeper. It can be used as a microphone but it resonates at about 4khz where it is most sensitive. It might be a piezo beeper that has a built-in oscillator (it continuously makes a high audio frequency tone when it has DC applied) which will not work as a microphone.

 

The piezo is what is suppling the input. If it does oscillate continuously that might explain why I am having so much trouble. I am limited to these components only. I don't have to do this circuit. It just seemed like a possibility.

 

I don't know and you don't know if you have a piezo transducer (speaker) that can also be a microphone, or a piezo beeper with a built-in oscillator that cannot be a microphone.

Here is the circuit for a "Keys Finder". When you whistle then it beeps. It can be modified to drive an LED instead of beeping. It uses a standard Cmos inverter (not a buffered gate) for amplifiers.