低功耗低位元能量高整合度之開關位移鍵接收機與
低功耗位元能量提升技術之開關位移鍵發射機
鄒京府* 李順裕**

國立成功大學電機工程學系研究所碩士班通訊暨生物積體電路設計實驗室
摘要
本論文根據 ISM Band 提出應用於身體感測網路系統之 2.4GHz 射頻發射機電路與接收機電路，因為是應用於穿戴式無線生理訊號檢測系統中，所以整體電路的設計都以低功耗、低面積為主要設計目標，達到延長使用時間，以及未來便於貼身以及植入的考量。論文中分成兩大部分，第一部分為 OOK 接收機，第二部分為 OOK 發射機。
論文的第一部分，創新且改良了接收機的兩大內部電路方塊。在封包檢測器與基頻放大器之中，採用創新電路架構，成功地在維持平方率接收機本身具低功耗與低面積的優點之下，進一步地提高了增益且加大了頻寬，且將單端轉雙端的 balun 整合入晶片設計中，進一步縮小面積。量測結果顯示，功耗為 11.1 W，靈敏度-46 dBm， 位元率 1 Mbps，位元能量 11.1 pJ/bit。
論文中的第二部分，為應用於身體感測網路之發射機設計，此發射機系統由三塊電路所構成:偏壓刺激電路、電流再利用自混頻壓控振盪器、四倍轉導增益功率放大器。其中在偏壓刺激電路中結合了一些 Delay 元件與開關的設計，可讓壓控振盪器在尚未起振時，瞬間提供壓控振盪器較大的偏壓電壓，並維持一段較短的時間後，再將刺激偏壓會回歸正常偏壓電壓，經由實行了此刺激之後，壓控振盪器就會比未刺激的情況下，具有更快的起振時間，而且壓控振盪器所消耗的功耗，會和未刺激的情況下是相近的，因此就能在消耗功耗極小的情況下，設計出一個起振時間更快的壓控振

盪器。在電流再利用自混頻壓控振盪器中，讓壓控振盪器與倍頻器做結合產生自混頻， 可使壓控振盪器在更小的偏壓電流之下，達到相同的相位雜訊規格。由於使用了電流再利用的技巧，壓控振盪器與倍頻器是共用同一個電流的，因此多使用倍頻器並不會增加功耗。本設計所提出的四倍轉導增益功率放大器，可以在單一的直流電流路徑下， 接收壓控振盪器的差動輸出訊號，並將訊號輸出至給天線，此功率放大器使用了雙重電流再利用的技術，因此所提出的功率放大器可以產生四倍的轉導增益(Gm)，相較於傳統的電流再利用架構，相同的偏壓電流只能產生兩倍的轉導增益輸出，因此本功率放大器就能成功地在極小的功耗之下產生極大的輸出功率。發射機的量測結果為，功耗為 0.81 mW，位元率 25 MHz，輸出功率 -14.2 dBm，位元能量 32.4pJ/bit。

A Low-Power, Low Energy-Per-Bit, High-Integrated OOK Receiver and a Low-Power OOK Transmitter with Energy-Per-Bit-Improved Technique
Ching-Fu Tsou Shuenn-Yuh Lee
Department of Electrical Engineering, National Cheng Kung University

SUMMARY
In this thesis, two RF chips with on-off keying (OOK) modulator/demodulator have been implemented for 2.4GHz ISM band. One is the OOK-receiver and another one is the OOK-transmitter. Because of the application in portable bio-signal detection system, low-power and low-area are the main concerns on the design, which can extend the usage time and improve the convenience of portability and implantation. There are two parts in this thesis, the first part is the OOK-Receiver, and the second part is the OOK-Transmitter.The first part of this thesis is the OOK- receiver for body sensor network with the square-law detection technique. With this modulation, the power consumption will be half because there is no power consumption while the system is passing the signal 0 and the circuit architecture is very simple, so the area of the chip will be smaller. In this thesis, the sensitivity and bit-rate will be improved by the proposed OOK-receiver. The second part of this thesis is the OOK-transmitter for body sensor network. The OOK-transmitter is made of the bias-stimulating circuit, current-reused self-mixing voltage-controlled-oscillator and the quadruple-Gm power amplifier. With these three novel circuit blocks, we can maintain the original advantage of the low power and low area of the OOK modulation, and improve the disadvantages of the low data rate and the low output power.

Key Word: RF transceiver, Body Sensor Network, On-off-keying modulation, Envelope detector, Baseband amplifier, Latch-Comparator, Harmonic detection, Self-mixing, Frequency doubler, Power amplifier, Current-reused
INTRODUCTION
In a general communication system, the power consumption is usually dominated by the RF-front-end. Hence, if we can decrease the power consumption of the RF-front-end, the lifetime of the battery will be increased. In order to transform the single-ended input signal

from Antenna to differential output signal, the balun with big area will be used to increase the xost of the chip. It will make against to the popularity of the wireless bio-signal acquisition system. Hence, in this thesis, a low power, low-area receiver and transmitter have been proposed. In the OOK-receiver, the active balun with self-biasing gain-bandwidth-improved envelope detector is proposed to overcome the drawback of large area implemented by passive balun. The proposed current-reused cascode-two-stage amplifier has the advantages of the two-stage amplifier with high gain and cascade amplifier with wide bandwidth. According to the proposed envelope detector and amplifier, an ultra-low-power receiver can be achieved.
In this OOK-transmitter, the bias-stimulating circuit (BSC) with the energy-per-bit- improved technique has been proposed. The self-mixing technique is implemented in the current-reused self-mixing voltage-controlled-oscillator (CRSMVCO) by the frequency-doubler and the cross-couple-mixer which are originally used in a traditional voltage controlled oscillator (VCO).The proposed quadruple-Gm power amplifier (QGPA), including two common-drain (CD) amplifiers and two common-source (CS) amplifiers, can achieve quadruple-gm but have the same power consumption as the traditional class-B power amplifier.
MATERIALS AND METHODS
In the OOK Receiver, the OOK modulated signal will be input to the matching network. Then the harmonic demodulation will be conducted in the square-law device. After the square-law demodulation, the high order harmonic part of the signal will be filtered by the low-pass filter. The proposed envelope detector is shown in Fig-1, and the current of square-law detector is derived as:

The AC part will be filtered out by the low-pass filter and the DC part is the demodulated signal of the input OOK signal.

After the demodulation, the amplitude of the signal is small. In order to amplify the signal to the level which can be detected by the comparator, a baseband amplifier is used ahead of comparator.The proposed amplifier has the advantages of the two-stage amplifier with high gain and cascade amplifier with wide bandwidth. Then the low power can be achieved without degrading the performance. The schematic of the proposed baseband amplifier is shown in Fig-2.

In the OOK Transmitter, the input digital data will be input to the BSC and the amplitude of the input digital data will be stimulated by the BSC at the first rising edge. Using BSC, the data-rate of the transmitter can be increased without increasing the power

consumption as comparing with traditional structures. The schematic of the proposed BSC is illustrated in Fig-3.

The schematic of the proposed CRSMVCO is shown in Fig-4. The cross-couple-mixer will carry out the down-frequency-conversion and generate a 2.45-GHz frequency and re-send it to the LC tank of the VCO as a positive feedback loop. With this positive feedback loop, the oscillation of the VCO will be strengthened, the amplitude of the resonant frequency will be increased and the power-efficiency of the power amplifier will be improved.

In the proposed Quadruple-Gm Power Amplifier (QGPA), the total transconductance is contributed by four MOSFETs, so the QGPA will produce quadruple-gm. With this technique, the power-efficiency of the transmitter can be improved. The proposed QGPA is shown in Fig-5.

RESULTS AND DISCUSSION
The proposed OOK-receiver has been fabricated in TSMC 0.18μm 1P6M CMOS process. Fig-6 shows the layout photograph of proposed OOK-Receiver. The chip area is 1.138 x 0.978 mm2.

The pseudo-random OOK input signal and the digital output signal are illustrated in Fig-7. The power of the pseudo-random OOK input signal is -50dBm and the amplitude of
the digital output signal is 1.2V. The bit-rate of the pseudo-random OOK input signal is 1Mb/s.

Conclusion
The proposed OOK-receiver includes balun envelope detector and baseband amplifier. The proposed OOK-transmitter is consisted of a BSC, a CRSMVCO and a QGPA. In order to comply with the requirements of body sensor network, the proposed circuits adopt OOK modulation in the transmitter and direct-up-conversion architecture in the receiver. The measured the power consumption in receiver is 11.1 W at the data rate of 1 Mb/s. The sensitivity and energy-per-bit are -46 dBm and 11.1pJ/bit, respectively. The measured the power consumption in transmitter is 0.81 mW with the output power of -14.2dBm and data rate of 25 Mb/s. Moreover, the energy-per-bit and power-efficiency are 32.4pJ/bit and 5.3%, respectively. It reveals that the proposed transceiver can be fitted in with the requirement of body sensor network for the bio-signal acquisition.

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