Analog IC Design First – A OPAMP Design Example.

Date: 15th NOV, 2007

報告人：何建興

22

AgendaAgenda

1. What is Analog Signal? 2. Elements Used in Electronic Products. 3. Why OPAMP. 4. How an OPAMP works. 5. What is MOS? MOS Basic

Characteristic. 6. A Design Example. 7. Is It the best design? 8. Is Direct Shrink Possible? 9. Q&A

33

What is Analog Signal?What is Analog Signal?

Analog signals in Integrated Circuits can be in the form of Voltage or Current (or Power).

They are continuous signals, (amplitude vs. time). Voice and Audio signals are good examples of analog signals.

If a threshold was set, then an Analog signal can be easily converted to Digital signal.

Example: A D AD_DA

44

Elements used in Electronic Elements used in Electronic productsproducts Resistors, Capacitors, Inductors,

Transistors and Diodes are basic devices (elements) in Integrated Circuit.

Many basic building blocks (IP) can be composed of these devices.

Ex: 1. RAM’s basic devices – MOS(RAM cell + logic circuit, sense Amp.) + Capacitors.

2. Logic circuit – CMOS. (PMOS + NMOS)

3. USB interface – MOS + Resistors.

55

Elements used in Electronic Elements used in Electronic products (continued)products (continued)

4. Recorder (ADC), Player (DAC) – MOS

+ Resistors + Capacitors. 5. Regulator – MOS + Resistors. 6. ESD PAD – MOS + Diode +

Resistors. The IP (Intellectual Property ) listed above are able to construct a MP3 player Chip.

Example: 1 2 3 4Many Analog blocks need OPAMP.

66

WHY OPAMP?WHY OPAMP?

1. OPAMP (Operational Amplifier) are one of the most important building blocks in Analog IC design. It can be used to do addition, subtraction, multiplication, logarithm, …operations.

Filters, Integrators, Oscillators Regulators, … etc. all include OPAMP.

Symbol of OPAMP Examples:

77

How An OPAMP Works?How An OPAMP Works?

1. There are 5 nodes on an OPAMP, they are Positive (V+) terminal, Negative (V-) terminal, Output (Vo) terminal, Power (VDD) and Ground (GND).

2. An ideal OPAMP characteristic: (I) infinite input resistance. (II) infinite open loop gain. (III) v+ = v- when negative feedback configuration.

88

How An OPAMP Works? How An OPAMP Works? (continued) (continued) 3. An real CMOS OPAMP can have:

(I) Very large input resistance (Ri) >1M ohm. input current =0 (II). Large but not finite open loop gain (A) > 1000 (60dB).

4. Examples: 5. Insight

99

What is MOS? MOS Basic What is MOS? MOS Basic Characteristic.Characteristic.

MOS : Metal –Oxide-Semiconductor Example

1010

A Design Example.A Design Example.

1. Specification: given a voltage 1.25V, design a OPAMP to achieve 2.5V output. Precision +- 1mV, : means A0>1000. settling time < 1us, means ft>1M.

2. Schematic:

1111

Is It the best design?Is It the best design?

1. The MOS size (aspect ratio) which we just designed is not the unique solution. We can do it better.

Based on the design we just finished, we can tune the MOS size to achieve: (i) smaller area (ii) consume less current. Both goals are the popular topic on SoC for the Cost issue.

They are many methods to optimize this design, only if they are immune to process variations.

1212

Is Direct Shrink Possible?Is Direct Shrink Possible?

1313

1414