CMOS problem, giving no input to a pin, should it suppose zero input (by default)??

[sfa732]

okay, yesterday i was trying to use CD4093 IC to use as Latch,, but it wasnt giving desired output, then i decided to test the I.C,,
I.C configuration is: there are 14 pins, 7th is ground and 14th is Vcc, pin 1 and 2 are for in, and 3 is its NAND output,
i test this IC using led, what i do is i onnct +ve leg of led to 3rd pin and -ve to 7th, then notice some results.!

a) when i connect both pin (1 and 2) to 14thpin (Vcc) it => LED didnt glow
b) i cnnect any of pin (1 or 2) to 7th pin (ground) and left remaining pin with no input => LED did glow
c) i connect both pins ( 1 and 2) to ground , => LED glow
d)i dont give any input to 1 and 2 pins, => LEd give random responses, continuosly glow on and off
e) i give Vcc to anyone input (1 or 2) and left the remaing pin => LEd give random responses, continuosly glow on and off


results a,b and c are fine,
but the problem i was facing was in result d and e, because when i give no input to any pin it should suppose to be given ground (by default) and LED shoul glow on, but this wasnt happening, LED was giving random responses... why is this happening?? plz reply plzzzzz, where i m doing mistake??

 

[rberek]

If you have unconnected inputs, the voltage will float and be influenced by circuit noise, etc. Therefore the outputs would be unpredictable, as you are seeing.

r.b.

 

[sfa732]

actually that day i was using a battery of 9 volt and 4 AA size battery of 1.5 volt in series when IC was doing problems,,
but i have done some test today as well,,
i use D.C power supply of 12 volt (made by me ) to connect I.C and it worked perfectly.......,,
now i am totally confused that why such thing is happening...,,
i dont want to use power supply,, i want to use battery,, ???

 

[std_match]

You must connect unused input pins to a "safe" voltage if they have any effect on your design.
Even if the inputs have no effect, they should be connected to '0' or '1' to avoid extra current consumption in the input stage.
The voltage on an unconnected CMOS input will not be stable, regardless of battery/power supply etc.

 

[godfreyl]

because when i give no input to any pin it should suppose to be given ground (by default)

No, there is no default. If you leave an input unconnected, the result is random.

All inputs should be connected to something. If you want the input low, connect it to ground. If you want it high, connect it to Vcc.