D1-2
A 120-mV Input, Fully Integrated Dual-Mode Charge Pumpin 65-nm CMOS for Thermoelectric Energy Harvester
Po-Hung Chen1, Koichi Ishida1, Xin Zhang1, Yasuyuki Okuma2, Yoshikatsu Ryu2,Makoto Takamiya1, and Takayasu Sakurai1
1

The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan
Semiconductor Technology Academic Research Center, 3-17-2 Shin Yokohama, Kohoku-ku, Yokohama 222-0033, Japan

2

Abstract - In this paper, a fully integrated low voltage charge
pump for thermoelectric energy harvesters is presented. The
proposed dual-mode architecture achieves both the low startup
voltage in a startup mode and high conversion efficiency in anormal operation mode without off-chip inductors andcapacitors. In the measurement, the proposed circuit successfully
converts 120-mV input to 770-mV output with 38.8% conversion
efficiency.

SFB
Operation
Oscillator

I

Selector
OperationI<7:0>10-stagedual-modecharge pump
Ij

Startup

VIN

CMOS switch
Diode for Dickson

Startup
Oscillator

I Introduction

DriverCK
Selector

VC

II System Architecture of Dual-Mode Charge Pump
The main challenges of the low input voltage charge pump
are low conversion efficiencyand small output current.Thelow conversion efficiency is caused by high threshold voltageof CMOS transistor (300-500mV). Operating under low
supply voltage makes the on-resistance of transistors increases
and decreases conversion efficiency. The small output current
is caused by low switching frequency. The low supply voltage
limits operation frequency. Since the available output currentof the charge pump is proportional to the switching frequency,
the low operation voltage limits the available output power.
Therefore, we proposed novel dual-mode architecture toovercome these problems.
Fig. 1 shows the block diagram of the proposed dual-mode
charge pump. It includes the startup oscillator,the operationoscillator, drivers, Iҏ selector (for gate switch), CK selector(for pumping switch) and the proposed 10-stage dual-mode
charge pump. The operation sequences of the proposed dualmode charge pump are illustrating in Fig. 2. At the startup

VOUT
SLOAD

Operation

The power management circuit applying thermoelectric
generators (TEG) for battery-freebody-wearable applications
is a focus of this paper. The output voltage of TEG is usuallyon the order of tens to hundreds of mV and is too low topower the electronic devices. To up-covert the harvested
energy to useable output, a low input voltage DC-DC
converter is required.
The key technique of such a DC-DC converter is thestartup mechanism, which kicks-start the system from low
input voltage. The previous works uses the boost converterwith additional startup mechanism such as mechanical switch[1] or charge pump [2] to kick start the system. The boost
converter requires large inductor and startup mechanism.
Therefore, area overhead is a problem.
To solve this problem, the ultra low voltage, fully
integrated charge pump is proposed. The novel dual-mode
architecture achieves both low startup voltage and highefficiency without off-chip inductors and capacitors.

978-1-4673-0772-7/12/$31.00 ©2012 IEEE

DriverCK<10:0>
Startup

CKj

CKj+1

COUT

RL

Fig.1 Block diagram of proposed dual-mode charge pump.
Startup by Dickson

Operation by CMOS switch
0.12V
0V

VIN

0.12V
0V
0.8V
0.5V
0.3V
0V
0.8VCKVCIVOUTSFB ONSLOAD ON0V
0.8V
0V

Fig.2. Operation sequences of proposed dual-mode charge pump.

mode, the input voltage VIN directly powers the startuposcillator and drives the charge pump with 120mV clock
amplitude through CK selector. The output capacitor COUT ischarged by charge pump and VC rises. As VC is charged to thepreset voltage (~0.3V), the switch SFB turns on and the charge
stored in COUT activates the operation oscillator. The Iҏ selector
and CK selector selects the signal from operation oscillator
and provided to the charge pump. The clock frequency andclock amplitude in operation oscillator is higher than that ofstartup oscillator (Startup: ~1MHz/120mV, Operation:~20MHz/770mV). Therefore, the COUT can be charged to thehigher voltage with high conversion efficiency. When VC ishigher than 0.5V, the switch SLOAD turns on and output voltage
is obtained. The switch SFB and SLOAD can be implemented byusing the voltage detector in [2].

III Implementation of Dual-Mode Charge Pump
The proposed dual-mode 10-stage charge pump combines
the 5-stage Dickson charge pump and 10-stage CMOS charge
pump. The simplified schematic and operation sequence isshown in Fig. 3. M1 and M2 forms Dickson charge pump andare used to charge COUT at startup as shown in Fig. 3(a). At
operation mode, the CMOS switches (M3-M6) are driven withhigh amplitude clock and on-resistance decreases as shown in469

Startup Operation

VIN

M1

M2

I1

I2

I2

I1
VOUT

M4

M3

VIN

M5

M6
COUT

CK1
CK1
CK2
CK2

CK1

0.12V
0V

CK1

0.12V
0V
0.12V
0V

CK2
CK2

0.12V
0V
0.8V
0V
0.8V
0V

I1I2(a)

M1

VIN

M1

I1

M2

I2I2

M3

M4

CK1
CK1(c)

M5

M6
COUT

M3

M5

M4

COUT(d)

870PP

900PP

0.40.224683020101000246810Output Power (PW)(b)

TABLE I
Performance comparison of fully integrated charge pump
Ref.

ISSCC’07[3]

ISSCC’09[4]

CICC’10[5]This work

CMOS
Process

350nm

350nm

65nm

65nm

VIN (min)

1V

0.6V

0.18V

0.12V

Efficiency

50%

70%

N/A

38.8%

No

Yes(2V battery)

NoNo(Dual-mode)

Externalexcitation

V. Conclusion
We have demonstrated a 120-mV fully-integrated charge
pump using novel dual-mode architecture. The dual-mode
architecture achieves both low startup voltage and highconversion efficiency at the same time without using
additional inductor/capacitor. It converts 120mV input to770mV output with 38.8% conversion efficiency. To the bestof our knowledge, it is the lowest operation voltage in CMOS
charge pump circuit.

References

M6Fig.4. Chip micrograph of proposed dual-mode charge pump.

0.6

V =0.16V
VIN=0.14V IN

This work was carried out as a part of the Extremely Low
Power (ELP) project supported by METI and NEDO.

Fig.3. (a) Simplified circuit schematic and (b) operation sequences ofthe proposed dual-mode charge pump. (c) Startup mode and (d)Operation mode.

Charge pump
Output(pumping capacitors) capacitors

VIN=0.12V

Fig.5. Measured dependence of (a) output voltage and (b) conversion
efficiency on output power.

VOUT
CK1
CK1
CK2
CK20.8

VIN=0.12V VIN=0.14V VIN=0.16V

40Output Power (PW)
(a)

I1

VOUT

1.0

Acknowledgments(b)M250

1.20.00IV. Measurement Results
The proposed circuit was designed and fabricated in 65nm
CMOS process. Fig. 4 shows the chip micrograph with active
area of 0.78mm2. Each pumping capacitor is 28.6pF and MIM
capacitor is used.
The measured dependence of the output voltage andconversion efficiency on output power is shown in Fig. 5. The
proposed charge pump successfully converts a 120mV input to770mV output with the conversion efficiency of 38.8%. Table
I compares the performance of fully-integrated charge pumps.
Ref [3] and [4] achieve high conversion efficiency but theoperation voltage is high. On the other hand, [5] achieves low
voltage operation but the conversion efficiency is low. The
proposed charge pump achieved the lowest operation voltage
with moderate conversion efficiency.

1.4

Efficiency(%)

Fig. 3(b). The first half stages of the CMOS charge pump isconstructed from the NMOS transistors (M3, M4) and the backhalf stages are constructed from PMOS transistors (M5, M6).
This scheme ensures the maximum overdrive voltage can beprovided to each transistor when gate is driven by highvoltage clocks (I). The transistors M1 and M2 are still
functional but most of the current flows through the CMOS
switch (M3, M4) because the on-resistance is much smaller
than that of diode connected MOSFETs (M1, M2). As a result,
the CMOS charge pump improves the conversion efficiency
while Dickson charge pump achieves low voltage startup.

Output Voltage (V)D1-2[1] Y. K. Ramadass and A. P. Chandrakasan, “A batterylessthermoelectric energy-harvesting interface circuit with 35mV startup
voltage,” IEEE International Solid-State Circuit Conference, pp. 486487, Feb 2010.
[2] P. Chen,et al., “A 95-mV Startup Step-Up converter with VTHTuned Oscillator by Fixed-Charge Programming and Capacitor PassOn Scheme,” IEEE International Solid-State Circuit Conference, pp.
216-217, Feb. 2011.
[3] H. Lhermet, C. Condemine, M. Plissonnier, R. Salot, P. Audebert,
and M. Rosset, “Efficient power management circuit: thermal energy
harvesting to above-IC microbattery energy storage,” IEEEInternational Solid-State Circuit Conference, pp. 62-63, Feb. 2007.
[4] I. Doms, P. Merken, R. Mertens, and C. Van Hoof, “Integratedcapacitive power-management circuit for thermal harvesters with
output power 10 to 1000μW,” IEEE International Solid-State Circuit
Conference, pp. 300-301, Feb 2009.
[5] P. Chen et al., “0.18-V input charge pump with forward bodybiasing in startup circuit using 65nm CMOS,” IEEE Custom
Integrated Circuit Conference, pp.239-242, Sep. 2010.

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