• Optimization of phase compensation constants

C1=1nF, C2=0.1μF

NULL Circuit → Fast and Stable

• Switching C1 and C2 depending on the measurement item

Settling time reduction → ≒ 1/10

オペアンプ試験技術Null法のシミュレーション・実測評価

青木里穂 片山翔吾 佐々木優斗 町田恒介 中谷隆之 王建龍 桑名杏奈 畠山一実 小林春夫

1. Research Objective

[1] J. M. Bryant, “Simple Op Amp Measurements”, Analog Dialogue, vol. 45. pp 21–23

(2011).

[2] Op Amp Applications Handbook, Analog Devices, (2004).

[3] K. Blake, “Op Amp Precision Design: PCB Layout Techniques”, Microchip

Technology Inc., Tech. Rep. AN1258 (2009).

[4] R. Dopkin, Analog Circuit Design, Linear Technology (2013).

[5] G. Robert, F. Taenzler, M. Burns, An Introduction to Mixed-Signal IC Test &

Measurement, 2nd edition, Oxford University Press (2012).

[6] Y. Sasaki, K. Machida, R. Aoki, S. Katayama, T. Nakatani, J. Wang, K. Sato, T. Ishida, T.

Okamoto, T. Ichikawa, A. Kuwana, K. Hatayama, H. Kobayashi, "Accurate and Fast Time

Testing Technique of Operational Amplifier DC Offset Voltage in μV-order by DC-AC

Conversion", IEEE 3rd International Test Conference in Asia, Tokyo (Sept. 2019).

References

5. Conclusion

4. SPICE Simulation Verification

Accurate and Fast measurement of

Operational Amplifier

For reliable and low-cost IoT systems

Approach

2. Background

-

+

Differential inputs Single-ended output

Extremely high gain

Operational Amplifier

Apply NULL method to mass production testing

Goal

Measurement time : Long

Mass production testing : Difficult

NULL Method

Good capacitor value selection

Fast, stable operation

VP

VN

Measured

Operational Amplifier

Auxiliary

Operational Amplifier

Operational Amplifier :

Vendor provided

SPICE model

3. NULL Method Prototype

Experimental Circuit

using NULL Method

Input sine wave

(1mVP-P , 1kHz)

Change

C1 and C2

C1=0.1μF, C2=0.1μF

1Hz 10Hz 100Hz 1kHz 10kHz 100kHz

30dB

-10dB

-50dB

60dB Vout

C1=1nF, C2=0.1μF

1Hz 10Hz 100Hz 1kHz 10kHz 100kHz 1MHz

36dB

0dB

60dB Vout

fc≅30Hz Slow

Optimal value :

C1=1nF, C2=0.1μF

fc≅1kHz Fast

< Offset Voltage >

Square wave input

(1μVP-P , 1Hz)

-

+𝑉𝑖𝑛+𝑉𝑖𝑛−

Ideal 𝑉𝑖𝑛+ = 𝑉𝑖𝑛−

In practice 𝑉𝑖𝑛+ ≠ 𝑉𝑖𝑛−

Vout=1mVp-p

0.0s 0.4s 0.8s 1.2s 1.6s 2.0s

0μV

400μV

200μV

-400μV

-200μV

-600μV

1μVP-P 1mVP−P

Easy Measurement

< CMRR >

RL [kΩ] CMRR [dB]

2 126

10 126

100 126

VP … +2.5V → +3.0V

VN … -2.5V → -2.0V

Vout=

500uVp-p1nF0.01uF

0.1uF

40ms 120ms 200ms 280ms 360ms

4mV

8mV

0mV

-4mV

-8mV

When RL=10kΩ, C1=1nF, C2 is varied

RL → 10kΩ, C1 → 1nF, C2 → Large

CMRR → Fast response

No.1 No.2 No.3 No.4 No.5

131 131 134 115 125

Experimental results (dB) for RL=10kΩ

NULL MethodMinus input voltage of amplifier

→ Zero potential with servo loop

< Frequency Characteristics >

30 times faster

Almost the same

Minute error → ×1,000

Measure

Simulation results

群馬大学 理工学府 電子情報・数理教育プログラム

ローム（株）

Fast

Key device in IoT systems

佐藤賢央 石田嵩 岡本智之 市川保