noise problem in ADC(atmega32)

atmega32 adc

I am having too much problems with noise in the in-built ADC of atmega32

Instead of external voltage I used internal 2.56 Vref and applied the voltage, then I am getting 2.55V for 2.24V. I used a capacitor of 150pf,22pf b/w AREF and ground.

I removed the multimeter probes from the breadboard, then a small difference came. But the noise is too much. My aim is to interface LM35 with atmega32. So I am just checking with a potentiometer.


Is there any way to avoid this noise

wht should be the value of capacitor b/w AREF and ground


My code

.cseg
.org 0x000
rjmp RESET



RESET:

ldi r16,0xff
out $11,r16 ;DDRD as output
out $12,r16 ; for checking if ADC is not good
out $17,r16
out $18,r16
rjmp ADC_INIT



ADC_INIT:

ldi r16,0b11100000 ; setting AD1,AD0 in ADCL
;internal 2.56 reference,Single
;channel A0
out $07,r16 ;setting ADMUX

ldi r16,0b10000101 ;setting control reg. ck/32
out $06,r16 ;setting ADCSRA

rjmp ADCSTART


ADCSTART:

sbi $06,6

WAIT:
sbis $06,4
rjmp WAIT

in r16,$04;ADCL
in r17,$05;ADCH

out $12,r17
out $18,r16
rjmp ADCSTART