Home > Products > Semiconductor > Design / Support > Product FAQs

Product FAQs

S/N: 10088 Last Updated: Apr 26, 2016

Why does it occur op amp output phase-reversal phenomenon?


An op amp same as input stage of NJM4558 might occur the output phase-reversal phenomenon. It is phenomenon that an output voltage will be stayed near high side rail immediately, when an input signal voltage is applied to exceeding the lower side common mode input range.

In case of exceeding input signal voltage to input common mode range, the op amp will occur an output phase-reversal phenomenon like Fig1.

Output  Reversal Voltage PhenomenonFig1 Output Reversal Voltage Phenomenon
Notes1: A solid line indicates input-output characteristics of NJM4558 at the voltage-follower circuit when it is occurred output reversal voltage.
A broken line indicates ideal input-output electrical characteristics.

An output phase-reversal phenomenon of op amp will be occurred by turned off Q5 and the Q6, as the following Fig 2.

Voltage follower application circuit with NJM4558 block diagramFig.2 Voltage follower application circuit with NJM4558 block diagramA broaken line is external connecting line
A The emitter terminal voltage of an initial-input stage amplifier circuit needs to be more than "Vbe Q5+Vbe Q6(≈1.4V)+VsatQ2" to V+ supply voltage as a reference to become active state for Q5/Q6. VsatQ2: the saturated voltage of Q2
B When the base voltage of Q5 falls, the Q5 and Q6 transistor of the next stage cut off. The output stage stays near V+ supply voltage side by connecting a current source to a corrector terminal of Q6.
C An active region voltage to operate Q5/Q6 should be applied about 1.4V DC.

An output stage buffer amplifier is stayed near V+ voltage side by current source connecting Q6.

Therefore, an output voltage of op amp stays near V+ voltage.
On Fig3, it is mentioned a typical characteristics of Input voltage versus Output voltage characteristics of NJM4558. A broken line is an ideal typical characteristics. A broken line is an actual typical characteristics.
This phenomenon might occur to NJM4558 series, but also to NJM2100. To operate within the Vicm of op amp is never generated this phenomenon.
You need to review about an input voltage condition if an op amp of your application has occurred an output phase-reversal phenomenon.

Input Voltage  VS. Output VoltageFig.3 Input Voltage VS. Output Voltage
Notes2: Input offset voltage vs. common mode input voltage typcal characteristics of dual supply op amp.

If it operates a dual power supply op amp at a single power supply voltage condition, this op amp might be occurred this phenomenon at the time of turning on power. A single power supply op amp is not occurred an output phase-reversal phenomenon at a dual supply voltage. Representative product name that causes this phenomenon is as follows.

Category: Operational Amplifier Devices: NJM2140,NJM2043,NJM2058,