user4833: I am using ATmega8A standalone but analog pins (Port C) have not been use.
Due to ATmega8A does not have a PRR (Power Reduction Register) to disable ADC and TWI.
I would like to know, is it a work around solution to reduce the power consumption if AVcc is not connected?

user42539: No, the datasheet says power must be connected to Avcc. This is from the '328P, Atmega8A is similar but with less memory:
(Microchip is taking forever to open the Atmega8A datasheet for me).

5.2.7  AVCC
  AVCC is the supply voltage pin for the A/D Converter (ADC), PC[3:0], and PE[3:2]. It should be externally connected to VCC, even if the ADC is not used. If the ADC is used, it should be connected to VCC through a low-pass filter.

https://www.microchip.com/wwwproducts/en/ATmega8A

user4143: No. You must connect AVcc even if you're not using the ADC.  According to the datasheet:

AVCC is the supply voltage pin for the A/D Converter, Port C (3:0), and ADC (7:6). It should be externally connected to VCC, even if the ADC is not used. If the ADC is used, it should be connected to VCC through a low-pass filter. Note that Port C (5:4) use digital supply voltage, VCC.


4833: <p>I am using ATmega8A standalone but analog pins (Port C) have not been use.</p>

<p>Due to ATmega8A does not have a PRR (Power Reduction Register) to disable ADC and TWI.</p>

<p>I would like to know, is it a work around solution to reduce the power consumption if AVcc is not connected?</p>
 42539: <p>No, the datasheet says power must be connected to Avcc. This is from the '328P, Atmega8A is similar but with less memory:
(Microchip is taking forever to open the Atmega8A datasheet for me).</p>

<blockquote>
  <p>5.2.7  AVCC
  AVCC is the supply voltage pin for the A/D Converter (ADC), PC[3:0], and PE[3:2]. It should be externally connected to VCC, even if the ADC is not used. If the ADC is used, it should be connected to VCC through a low-pass filter.</p>
</blockquote>

<p><a href="https://www.microchip.com/wwwproducts/en/ATmega8A" rel="nofollow noreferrer">https://www.microchip.com/wwwproducts/en/ATmega8A</a></p>
 4143: <p>No. You must connect AVcc even if you're not using the ADC.  According to the datasheet:</p>

<blockquote>
  <p>AV<sub>CC</sub> is the supply voltage pin for the A/D Converter, Port C (3:0), and ADC (7:6). <strong>It should be externally connected to V<sub>CC</sub>, even if the ADC is not used.</strong> If the ADC is used, it should be connected to V<sub>CC</sub> through a low-pass filter. Note that Port C (5:4) use digital supply voltage, V<sub>CC</sub>.</p>
</blockquote>
