Mystery on IC mixer Circuit

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1

Hello all,

First post being made here

I am making a mixer to connect two oscillators into. I am using a ttl 73LS266n chip for the mixer. Two oscillators are from 74LS132 chip.

For some odd reason the mixer chip doesn’t work. It’s an XNOR chip. The frequencies are coming in properly. I connect it to a nand gate and it works fine. Even looking at the unused gates, the inputs are grounded and outputs aren’t. Since it is an XNOR gate, 2 lows should yield a high output on the unused ones. I’m receiving a very low output on all of the pins. It is very mysterious. I ordered two of same IC and problem existed with both ICs.

Please solve my mystery. thank you

2

Have you accounted for the fact this chip has an open collector output and would need a pull-up?

3

uh… no

How do i do that. I thought it was just an XNOR. Isn’t open collector a NOT gate.

I don’t fully understand what an open collector is.

4

Do a web search (google or Wikipedia) and read to learn what ‘open collector’ is.

5

What pull up resistor do i need to use. How can i calculate my impedence if i don’t know my current

6

Look in the data sheet for Iol (low level output current). This give you the limit for the pull-up minimum resistance value.

Now what is this output driving? The pull-up needs to produce a logic high level into the receiver and must do it fast enough to have clean rising and falling edges.

Many times the value is determined empirically.

7

So since my loL is a max of 8mA, my pull-up resistor will be 5/.008 which is 625. Now this is my minimum resistance value.

Now i’m assuming i have to take a multiple of this value.

How do i do this.

8

Without knowing more about what you’re doing I’d suggest just going with about 2,000 ohms. If you’re just driving another gate input then 10,000 ohm will be fine. If you’re directly driving an LED, speaker or several meters of wire then go with 1,000 ohms.

9

I would suggest just using a XNOR with push-pull outputs such as 74HC7266D,653 (Digikey# 568-8163-1-ND). Feeding two oscillators into an XNOR would be considered a phase detector (with a low-pass filter on the output) rather than a mixer, is that what you’re expecting?