1. An Oscillator Design Based on Bi-CMOS Differential Amplifier Using Standard SiGe Process Cher-Shiung Tsai, Ming-Hsin Lin, Ping-Feng Wu, Chang-Yu Li, Yu-Nan Yeh, Wu-Yan Sie, Kwang-Jow Gan, Pei-Hua Chang, Dong-Shong Liang, Jin-Wei Wu and Chia-Hsiang Chang Department of Electronic Engineering, Kun Shan University Tainan, Taiwan 710, R.O.C. TEL: (06)2050521 EXT1805, FAX: (06)2050250, EMAIL: e5040@mail.ksu.edu.tw 1.Introduction We use the high input resistance, high output resistance and high voltage gain characteristics of Bi-CMOS differential amplifier [1-3] to create an oscillator. Such oscillator is based on differential amplifier cascades two inverters. We connect one CMOS inverter and the other CMOS inverters output with two different inputs. It is an symmetric structure and most output waveform tends to be sine waveform. The oscillator frequencies are decided by NPN transistor hFE value, active load PMOS and CMOS inverters time delay. The oscillator circuit was implemented by CIC standard 0.35 um SiGe process. The oscillator oscillates from 80 MHz to 400 MHz under 1.1 volts to 3.3 volts. The working frequency includes VHF and UHF range. In this thesis, we present a different type oscillator and use experimental results to prove such oscillator is useful, easiness and flexibility in design. Fig.3 Oscillator (Right-upper corner) IC photograph 2. Circuit Theorem and Simulation The oscillator is composed of Bi-CMOS differential amplifier by adding two CMOS inverters as shown in Fig.1. A formal differential amplifier needs a constant current source but we use NMOS to replace constant current source for simplicity. According to differential amplifier operation, transistor Q1 and Q2 can’t be off in the same time. Transistors Q1, Q2 will both be in on state or one is on and the other is off. In the meanwhile, transistor Q1 or Q2 can’t be in saturation state. Because we can’t fabricate two identical transistors Q1 and Q2, so most conditions are Q1 on and Q2 off, or Q1 off and Q2 is on. We transform Fig.1 into Fig.1-A for simplified logic level. Those initial values of V+ 、 V- and VO are listed in Table1. State1 or state2 will change into State3 and State3 will switch to State4. The next is State4 changes back to State3. It will toggle itself between State3 and State4. Such continuous toggle phenomena will cause oscillation. We use CIC standard 0.35um SiGe process parameters to run H-spice simulation of Bi-CMOS differential amplifier oscillator. While under 3.3 volts supply voltage, NMOS or PMOS is minimum channel width then the output oscillation frequency is merely 800 MHz as shown in Fig.2. Fig.1 The Bi-CMOS differential amplifier oscillator Fig. 1-A Simplified Logic Level of Fig.1 Fig.4 Oscillator test module. Fig.5 Output spectrum under 3.3 volts Fig.5 is the spectrum diagram of the Bi-CMOS differential amplifier oscillator. The highest signal is more than the other signals about 80 db in Fig.5. It means the main oscillation signal is ten thousand (1080/20=10000) times stronger than the noise signals. Fig.6 is the phase noise diagram of the Bi-CMOS differential amplifier oscillator. Fig.6 shows the oscillator with low noise characteristics from 1 KKz to 10 MHz. The phase is -111.85 dbc/Hz under 1 MHz. In post simulation, the Bi-CMOS differential amplifier oscillator shows nice VCO linearity from 1.1 volts to 3.3 volts supply voltage as shown in Fig.7 but real IC oscillator is not match to simulation results. 4. Conclusions The Bi-CMOS differential amplifier oscillator is the same as general oscillators that the noises are proportional to output frequencies. But the Bi-CMOS differential amplifier oscillator still has low noise and excellent voltage controlled (VCO) characteristics. We will improve the disadvantages by IC implementation. CMOS inverter will become short time delay in CIC process and PMOS will be modified. If we can implement Bi-CMOS differential amplifier oscillator into IC chips, then we will achieve improvements in frequency response to deeper UHF band, voltage control characters, power consumptions and noise performance. Acknowledgements The authors would like to thank the National Science Council of Republic of China for their kind support. This work was supported by the National Science Council of Republic of China under the contract no. NSC97-2221-E-168-046. References [1]Donald A Neamen “Electronic Circuit Analysis and Design,” 2 nd edition, pp. 688-690, 2001. [2]Richard C. Jaeger and Travis N. Blalock, “Microelectronic Circuit Design,” 2 nd edition, pp. 1087-1108, 2003. [3]Adel S. Sedra and Kenneth C. Smith, “Microelectronic Circuits,” 5 th edition, pp. 687-719, 2004. V+V-VOVO State1HHL State2LLL State3HLH State4LHL Table.1 States of Fig.1-A Fig2. Output waveform of pre-simulation result 3. Experimental Results In this thesis, we use spectrum analyzer to measure oscillator. Fig.3 is IC photography, the Bi-CMOS differential amplifier oscillator is on right upper position. Fig.4 is th oscillator test module. The output spectrum under 3.3 volts supply voltage and oscillation frequency is 480 MHz as shown in Fig5. Fig.6 Phase noise diagram of Fig.1 Fig.7 VCO characteristics of Fig.1