Folded Cascode Amplifier
Detection of Bioelectric Signals with AFE
姜禮夫, 孔令洋 指導教授:洪崇智
Department of Electrical and Computer Engineering, National Yang Ming Chiao Tung University, Taiwan
ABSTRACT
Over the past few years, there has been a remarkable surge in the fascination surrounding the detection of signals originating from the human body. These
signals, known as bioelectric signals, serve as a manifestation of the synchronized electrochemical activity within the nerve cells. However, the magnitude of
these bioelectric signals tends to be relatively minuscule. To obtain bio-signals with enhanced precision and alleviate the burden on the ADC, the integration
of an Analog-Front-End (AFE) becomes imperative.
INTRODUCTION
CIRCUIT
The AFE acts as an amplifier, magnifying the bio-signals
High-swing cascode current mirror :
Folded cascode amplifier:
and enabling high-resolution acquisition.
It should meet:
1. Low-power consumption
2. Low-noise
3. Enough slew rate
Fig.1 AFE.
Fig.2 op-amp circuit.
Our goal is to design the op-amp that works
Our target:
well and meet the conditions above.
This op-amp
The High-swing cascode current mirror makes proper bias voltage for the Folded cascode amplifier, and then the
Folded cascode amplifier amplified small signals without distortion for effective signal amplification and stability.
SPEC CALCULATION
PERFORMANCE TABLE
● Gain = gm*Rout > 80dB = 10000 V/V
(Our: Gain = 12022 V/V)
● GBW = gm/CL > 30K ⇒ gm > 377nA/V
(Our: gm = 430nA, GBW = 29.6k)
● Slew rate = dV / dt = 2I / CL > 1000 (V/sec)
⇒ I > 1nA
● gm = 2I / Vov with Vov = 0.2v ⇒ I = 38 nA
● Rout = Gain / Gm > 26.5G ohm
● ω3dB = GBW / Gain = 6π rad/s
Table.1 Bias Performance.
● Output swing = 1.8 - 2Vovp -2Vovn
= 1.8 - 4*0.2 = 1V
Table.2 SPEC Performance.
SIMULATION RESULTS
Fig.3 Gain and GBW.
Fig.4 Phase Margin.
Fig.5 Slew Rate.
Fig.6 Output Swing.
CONCLUSION
Throughout the course of this project, we have gained valuable knowledge in practical circuit applications and analog circuit simulation. By
delving into the theory behind these circuits and putting textbook concepts into practice, we conducted numerous tests and experiments. Through
hands-on experience and simulations, we observed and learned a multitude of valuable insights. Ultimately, our final project involved successfully
implementing and testing an op-amp, examining its stability and functionality. While we met most of the SPEC requirements, we recognized that
our unity-gain bandwidth fell short. To further enhance its performance, we may explore options such as increasing the gm or reducing the load
capacitance. We extend our sincere gratitude to our professor and teaching assistants for their invaluable guidance throughout this journey.
NYCU ANALOG IC LAB
NYCU ANALOG IC LAB