Cirrus Logic AN300 REV1 - Manual (Page 8)

8 AN300REV1
AN300
Figure 11. Open-loop Gain and Phase vs. Frequency, CS3001/02/11/12 (Expanded)
In applications that require a small signal (< 10 mV) to be amplified by a large gain (> 200X) the very high open
loop gain of the CS3001/2/11/12 amplifiers ensures gain accuracy and excellent linearity.
Figure 12 compares the
open loop gain of the CS3001 to an operational amplifier with 120 dB of open loop gain where the amplifiers are
configured for a gain of 400X (52 dB). If the CS3001 is configured for a gain of 400X (52 dB), the amplifier has 248
dB of loop gain (300 - 52 = 248) to ensure gain accuracy and to reduce linearity errors. 248 dB is a factor of 2500
billion. This appears to be excessive until one understands that the CS3001 was designed to achieve 20-bit linear-
ity with a 1 kHz sine wave when set for a closed loop gain of 30X.
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