Operational amplifier and scanning electron microscope using the same
View Patent ↗An operational amplifier and a scanning electron microscope which are capable of dealing with high voltage and large current, and which allow implementation of stable and precise amplification, the operational amplifier having a first-stage amplification unit including a differential pair, a base-grounded amplification circuit, and an active load, the base-grounded amplification circuit being cascode-connected to the differential pair a second-stage amplification unit including an inverter having an emitter follower circuit and a constant-current load circuit, and a third-stage amplification unit including a source follower circuit or an emitter follower circuit.
1. A scanning electron microscope, comprising:
an electron source,
a deflector for deflecting an electron beam emitted from said electron source, and
an amplifier for amplifying a signal to be supplied to said deflector,
said amplifier, comprising:
a first-stage amplification unit including a differential pair, a base-grounded amplification circuit which is cascode-connected to said differential pair and an active load connected to the base-grounded amplification circuit, and
a second-stage amplification unit connected to said first-stage amplification unit, and including an emitter follower and a constant-current load circuit for said emitter follower,
wherein said active load comprises a Widlar-type current mirror circuit having a ballast resistor.
2. The scanning electron microscope according to claim 1 , further comprising:
a third-stage amplification unit including a source follower circuit or an emitter follower circuit.
3. The scanning electron microscope according to claim 1 , wherein voltage applied to said ballast resistor is equal to 0.3 V or more.
4. The scanning electron microscope according to claim 2 , wherein voltage applied to said ballast resistor is equal to 0.3 V or more.
5. A scanning electron microscope, comprising:
an electron source,
a deflector for deflecting an electron beam emitted from said electron source, and
an amplifier for amplifying a signal to be supplied to said deflector,
said amplifier comprising:
a first-stage amplification unit including a differential pair and a base-grounded amplification circuit which is cascode-connected to said differential pair, and
a second-stage amplification unit connected to said first-stage amplification unit, and including an emitter follower and a constant-current load circuit for said emitter follower,
wherein said base-grounded amplification circuit of said first-stage amplification unit is connected to a capacitor.
6. The scanning electron microscope according to claim 5 , further comprising:
a third-stage amplification unit including a source follower circuit or an emitter follower circuit.
7. The scanning electron microscope according to claim 5 , wherein a diode or a resistor is connected to connection portion between said capacitor and said base-grounded amplification circuit of said first-stage amplification unit.
8. The scanning electron microscope according to claim 6 , wherein a diode or a resistor is connected to connection portion between said capacitor and said base-grounded amplification circuit of said first-stage amplification unit.
9. A scanning electron microscope, comprising:
an electron source,
a deflector for deflecting an electron beam emitted from said electron source, and
an amplifier for amplifying a signal to be supplied to said deflector,
said amplifier comprising:
a first-stage amplification unit including a differential pair and a base-grounded amplification circuit which is cascode-connected to said differential pair, and
a second-stage amplification unit connected to said first-stage amplification unit, and including an inverter having an emitter follower and a constant-current load circuit for said emitter follower,
wherein an emitter load of said inverter comprises a diode.
10. The scanning electron microscope according to claim 9 , further comprising:
a third-stage amplification unit including a source follower circuit or an emitter follower circuit.