OPA2325 Datasheet, PDF (15/32 Pages) Texas Instruments – Precision, 10-MHz, Low-Noise, Low-Power, RRIO, CMOS Operational Amplifier

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OPA2325
SBOS637 – OCTOBER 2016
7.3 Feature Description
7.3.1 Zero-Crossover Input Stage
Traditional complementary metal oxide semiconductor (CMOS) rail-to-rail input amplifiers use a complementary
input stage: an N-channel input differential pair in parallel with a P-channel differential pair. This configuration
results in sudden change in offset voltage when the input stage transitions from the p-channel metal-oxide-
semiconductor field effect transistor (PMOS) to the n-type field effect transistor (NMOS), or vice-versa, as shown
in Figure 40. This transition results in significant degradation of CMRR and PSRR performance of the amplifier.
.
3
2
1
0
-1
-2 _-V
+V
-3
-0.5 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
Input Common-Mode Voltage (V)
Figure 40. Input Common-Mode Voltage vs Input Offset Voltage
(Traditional Rail-to-Rail Input CMOS Amplifiers)
The OPA2325 amplifier includes an internal charge pump that powers the amplifier input stage with an internal
supply rail that is higher than the external power supply. The internal supply rail allows a single differential pair to
operate and to be linear across the entire input common-mode voltage range, thus eliminating crossover
distortion. Rail-to-rail amplifiers that use this technique to eliminate crossover distortion are called zero-crossover
amplifiers.
The single differential pair combined with the charge pump allows the OPA2325 to provide superior CMRR
across the entire common-mode input range, which extends 100 mV beyond both power-supply rails. Figure 41
shows the input offset voltage versus input common-mode voltage plot for the OPA2325. Note that unlike
traditional rail-to-rail CMOS amplifiers, there is no transition region for the OPA2325.
150
125
100
75
50
25
0
±25
±50
±75
±100
±125
V_CM = ±2.85 V
V_CM = 2.85 V
±150
±3
±2
±1
0
1
2
3
V_CM (V)
C003
Figure 41. Offset Voltage vs Common-Mode Voltage (Zero-Crossover)
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