Well, first of all, A5 is not an analog OUTPUT pin, analog INPUT only.
Second, if you have a regular RC servo, the PID is already built into the control electronics and is controlled by a PPM signal from a digital pin by a servo library like the Arduino Servo library (Google "Arduino servo").
8 bit Arduinos don't have "real" analog output but simulate it by switching certain pins (3, 5 ,6 , 9, 10 & 11 ) on & off rapidly. It's called PWM or pulse width modulation.