A feedback is said to be positive if the signal causes further increase or amplification in the magnitude of the output signal instead of stabilizing the signal. For this reason, it can be referred to as regenerative feedback. Negative feedback exists when the output of a system operates to oppose changes to the system input, thereby causing less modification while the feedback signal decreases. This is also known as a self-correcting or balancing loop. Negative feedback is typically used to increase the accuracy and stability of a system by correcting unwanted changes while positive feedback causes the amplifier to increase its internal gain by having the same phase as the input signal. Since positive feedback is useful only in exceptional circumstances, it is rarely useful in amplifiers while negative feedback is useful in setting the parameters of an amplifier like the input and output impedance, stability and bandwidth, and voltage gain. Both positive and negative feedback require a feedback loop to operate for its control of the system.