Power Supply Rejection Ratio (PSRR) is a critical parameter in voltage regulators that measures their ability to reject fluctuations and noise present in the input power supply. It is an essential characteristic, especially in sensitive electronic circuits where a stable and noise-free power supply is crucial for proper operation.
The PSRR is defined as the ratio of the change in the output voltage of the regulator to the change in the input voltage. It is usually expressed in decibels (dB). The formula for PSRR is as follows:
PSRR (dB) = 20 * log10 (∆Vout / ∆Vin)
Where:
∆Vout = Change in the output voltage of the regulator
∆Vin = Change in the input voltage to the regulator
The higher the PSRR value, the better the voltage regulator can reject changes in the input voltage and maintain a stable output voltage. For instance, if a voltage regulator has a PSRR of -60 dB, it means that for every 1 mV change in the input voltage, the output voltage will only change by 1 µV (because -60 dB is equivalent to a ratio of 0.001).
The significance of PSRR lies in its impact on noise performance in electronic circuits. Here's why PSRR is crucial for noise performance:
Noise Rejection: In electronic systems, there can be various sources of noise, such as switching noise from other components, electromagnetic interference, or power supply fluctuations. The PSRR of the voltage regulator helps attenuate these noise sources from the power supply before they reach sensitive components. A higher PSRR value means better noise rejection and a cleaner power supply for the rest of the circuit.
Signal Integrity: Noise on the power supply can couple into the signal path of the circuit and degrade signal integrity. For example, in analog-to-digital converters (ADCs) or analog circuits, power supply noise can appear as unwanted voltage variations in the output signal. By having a voltage regulator with high PSRR, the impact of power supply noise on the circuit's performance can be minimized.
Stability: Some electronic circuits are very sensitive to changes in the power supply voltage. High PSRR ensures that the voltage regulator can maintain a stable output voltage even when the input voltage fluctuates. This stability is vital for the proper functioning of the circuit and can prevent issues like malfunctions, data errors, or damage to sensitive components.
Minimizing System Noise Floor: In many electronic systems, the overall noise performance is limited by the noise floor. Power supply noise can contribute significantly to this noise floor. A voltage regulator with good PSRR can help reduce the power supply noise contribution, leading to an overall improvement in the system's noise performance.
In summary, the power supply rejection ratio (PSRR) is a critical parameter in voltage regulators as it directly affects the noise performance of electronic circuits. A higher PSRR value indicates better noise rejection, improved signal integrity, and enhanced stability, making it an essential consideration when selecting voltage regulators for noise-sensitive applications.