Many friends said that they want more interview questions in the direction of analog IC, so this is it! (All interview questions are available at the end of the article )
1. How many kinds of feedback are there in Bandgap? The principle is?
Positive and negative feedback.
2. What kind of negative feedback? Advantages of negative feedback?
Types : Voltage parallel feedback, current series feedback, voltage series feedback and current parallel feedback
Advantages : reduce the gain sensitivity of the amplifier, change the input resistance and output resistance, improve the linear and nonlinear distortion of the amplifier, effectively expand the passband of the amplifier, automatically Regulatory effect.
3. Observe the circuit diagram, what is the function of M2 in the diagram? What is the function of M3 in the figure?
Derives the value of Rout.
1) The role of M2 is to act as the cascode tube of M1 to increase the output impedance.
2) The function of M3 is gain boosting.
3) The value of Rout is: gm2rout1rout2gm3rout3.
4. Talk about your understanding of matching and what you need to pay attention to
Matching is a characteristic in which performance changes between components are consistent, and performance changes have a constant ratio. Horizontal matching,
vertical matching, center matching.
Note :
1. Keep the direction of the device consistent
2. The devices that need to be matched are close to each other (as compact as possible, using source-drain sharing technology)
3. Keep away from high-power devices
4. Choose an intermediate value as the root device
5. Use
interdigitation
6. Surround with virtual device Duming
7. Ensure symmetry (axis symmetry and center symmetry)
8. Match the parasitic
parameters of the wiring consistent
9. Make the differential wiring consistent
10. Make the device width consistent
11. Avoid routing on the matching device
12. Overall is to communicate with the circuit designer
5. Resonance of the circuit
If the frequency of the external AC power supply is the same as the natural frequency of the LC loop, the current generated in the loop is the largest, and the
magnetic field energy in the loop L and the electric field energy in C just form a self-contained system, exchange inside the circuit, and maximize the power from the power supply. Absorbing energy without returning energy to the power source is called resonance.
6. What is a capacitor?
Capacitors are a class of passive devices used to couple AC signals and build delay and phase shift networks. Capacitors store electric field energy.
7. What is a bypass capacitor?
Capacitors that can leak high-frequency components in alternating current mixed with high-frequency currents and low-frequency currents are called "bypass capacitors".
8. What is the essence of the push-pull structure?
Generally, it means that two triodes are respectively controlled by two complementary signals, and when one triode is turned on, the other is always turned off.
To realize the line and need to use OC (open collector) gate circuit. If there are two transistors in the output stage, one is always on
and the other is off, that is, the two transistors are connected by push-pull. This circuit structure is called a push-pull circuit or
Totem-pole output. circuit.
9. What are parasitic effects and what are the main parasitic effects? How to prevent parasitic effects?
The parasitic effect is in the non-ideal state, which is not expected to exist in the design, the
new characteristics produced by the characteristics of the material itself, or the mutual influence and action between the materials and materials under specific conditions, and these characteristics form virtual objects in the layout. These
virtual devices have some or all of the functions and characteristics of real devices. These devices do not exist in the circuit diagram, but they are
equivalent to "real" existence in the layout, which will affect the performance of the chip.
So in the layout we should try to avoid parasitic effects.
Parasitic resistance: widen the width of the corresponding layer.
Parasitic MOS tube: High-level metal wiring is used, and high-voltage signals do not pass through the device as much as possible.
Parasitic diode: It is basically unavoidable, and specific problems need to be analyzed in detail, and layers can be added through the process, such as NBL isolation.
Parasitic triode: It is basically unavoidable, and specific problems need to be analyzed in detail, and layers can be added through the process, such as NBL isolation.
10. Where Latch up is prone to occur
1) Latch up is prone to occur in places where high-frequency signals are connected to devices.
2) Latch up is prone to occur in and around places where the substrate has large current fluctuations.
3) Where the high-voltage well and the low-voltage well are mixed, especially when the well potential may be close to or lower than the ground potential,
latch up is prone to occur.
4) ESD-connected devices are prone to latch up.
Due to space limitations, I will not update them one by one. Students who need the above interview questions can get them on demand and share them with everyone~
Let me put it here: Analog IC pen interview questions