Slew Rate of PGA4311 & PGA2310

Hello,

The slew rate of the PGA4311 and PGA2310 is high enough such that it has no measurable effect on linear audio performance. There is a common misconception that faster slew rate means less high frequency distortion in linear operation. Please keep in mind that a slew rate-limited response only occurs during completely non-linear operation of the amplifier and is not an indicator of how linear an op amp (specifically its input stage) is below the slew rate. 

Consider that for a bandwidth limited system, the maximum bandwidth of the system also determines the fastest rise time it can have. For example, an audio system with a DAC sampling at 192 kHz has a maximum bandwidth of 96kHz. The relationship between bandwidth and rise time is: T(rise) = 0.35 / Bandwidth. So for a system with a 96kHz bandwidth, the fastest rise time possible is 0.35 / 96kHz = 3.646 microseconds. If the op amp is powered from +/-15V supplies, and had to step all the way from the negative supply to the positive supply (neglecting output voltage swing limitations) the fastest rate of change possible is this system is 30V / 3.646 microseconds = 8.23 Volts per microsecond. This is the fastest rate of change possible, limited by the system bandwidth and power supplies, not the op amp slew rate. This analysis also doesn’t include the bandwidth limitation of the human ear.

Despite the common misconception, most high frequency distortion in op amps is really determined by the op amp output stage linearity. This is a constant error source in the feedback loop of the op amp, and as the loop gain decreases this distortion rises above the noise floor of the measurement. 

Best regards,

Ian Williams
Linear Applications Engineer
Precision Analog - Op Amps