The Design of 0.35um Smith Sawtooth Generator

The Design of 0.35um Smith Sawtooth Generator Yuan-Paio Lee ChienKuo Technology University, ChungHua, Taiwan, ROC ABSTRACT In this study, the use of the relaxation oscillation theory, successful design improved Smith circuit sawtooth wave generator. The oscillator is used to generate the analog signal having a periodic electronic circuit. Usually by the amplifier circuit, frequency-selective network, both positive and negative type feedback network and Leveled links. The oscillator can be mainly divided into: the harmonic oscillator and relaxation oscillator. In this study, using the National Chip Implementation Center of Taiwan Semiconductor Company standard 0.35μm process, which is two layers of polysilicon and four metal layers. Be improved based on the single-stage operational amplifier, and using cascaded current source, to design a high-gain operational amplifier. High gain operational amplifier with the Schmitt theory is designed sawtooth wave generator. Finally, research to improve sawtooth wave generator RC charging and discharging part, achieve high linearity Smith circuit. Keyword: HSPICE, Smith, RC charge and discharge, OPAMP, sawtooth wave oscillator I. INTRODUCTION Sawtooth has a wide range of uses, such as multi-dof legs robot, telephone quality signals, robust adaptive control, and voltage balancing strategy of a five-level flying capacitor converter.[1-4] Oscillator is used to generate an electronic circuit having a periodic analog signal. The analog signal is usually sine wave or square wave. Oscillator usually is composed by the amplifier circuit, frequency-selective network, both positive and negative type feedback, and network Leveled part of the composition. Low-frequency oscillator (LFO) means to generate a frequency of between 0.1 to 10 Hz AC signal oscillator. It is usually used in audio synthesis, and used to distinguish the audio oscillator. The oscillator can be mainly divided into the following two groups: the harmonic oscillator and the relaxation oscillator. The basic principle of the harmonic oscillator is the output of the filter to the amplifier, again the output of the amplifier through the feedback circuit connected back to the input of the filter. Instantly, when the power supplied, the 1

amplifier output is only noise. The noise is transmitted to the filter, so that the noise of a specific frequency to be filtered out, and appears in the output of the filter. Also received the input of the amplifier because the output of the filter, so the filtered signal is amplified through an amplifier, and then into the filter circuit filtering, until the output signal is just until the signal that we want. The piezoelectric effect of the crystal (usually refers quartz) can be used as the filter and the amplifier is coupled. This oscillator is referred to as a crystal oscillator. It has a fairly stable oscillation frequency. Implement the harmonic oscillator, can be used with different amplification and filtering, so there are many different implementation method: Hartley oscillator, Colpitts oscillator, Clapp oscillator, Pierce crystal oscillators, the phase shift oscillator, RC oscillator (Wien-Bridge oscillator with a double T) LC oscillator. The relaxation oscillator is mainly used to produce non-sine wave output signal, such as a square wave or sawtooth wave. The relaxation oscillator containing a periodic nonlinear element such as transistors like the energy stored in a capacitor or inductor released so that the output signal waveforms instantly change. Relaxation produces a square wave oscillator can be used in the clock signals of the sequential logic circuit (such as: timers, counters), although usually will often choose the more stable crystal oscillator clock signal. Output sawtooth wave generator (or sawtooth) is usually used in time-based signal generated in an oscilloscope or cathode ray tube television horizontal reflector. In the frequency generator, the sawtooth wave is also used to integer close to a sine wave signal to output. The relaxation oscillator is a multivibrator (complex oscillator). 555 of the timing of integrated circuits is a very versatile integrated circuit, a lot of the sawtooth wave generated by it. In 197, Signetics Corporation creates the future of the first to come out timer dedicated IC, 555. Since price is low, therefore, the chip is widely used in automatic control circuit. The chip, 555, of the interior is composed of many transistors, diodes and resistors. For application-specific integrated circuit and does not need detailed study its internal circuit action principles, just to understand its pin function can be applied easily. Nevertheless, Integrated circuit design, coupled with a 555 timer plot circuit very space and totally inconsistent with the principles of the chip design and production costs. In this study, the use of the National Chip Implementation Center, CIC, Taiwan Semiconductor Manufactor Co., TSMC standard 0.35μm process, it is two layers of polysilicon and four metal layers (P4M:-Polysilicon 4-Metal). Based on the single-stage operational amplifier to be improved and use of the cascade current source

(Cascade Current Mirror), the design of the high-gain operational amplifier, with a Schmitt circuit design sawtooth wave generator. Finally, improved Smith circuit sawtooth wave generator generates a sawtooth wave of high linearity. A total of six sections in this article: the first section is the introduction. Section two is Introduction to the use of differential configuration op amp. The third quarter is to explore research Schmitt circuit. The fourth quarter results and discussion; the constructivist design Schmitt circuits and improved, and attach the simulation results. Finally, Section V is the conclusion. II. OPERATIONAL AMPLIFIER Operational amplifier (OP, OPA, OPAMP) is a DC-coupled, differential mode input, usually for a single-ended output, high gain voltage amplifier. Operational amplifier is widely used in home appliances, industries, and scientific instrumentation field. In the current technology, many operational amplifiers are built by CMOS devices. In the application, the operational amplifier can be divided into a negative feedback configuration, as well as positive feedback impedance. Negative feedback impedance magnification sacrificed in exchange for the stability of the circuit work also inhibited the many benefits of the external noise interference. Positive feedback impedance compared to the need to generate shock signal system, which is fairly common of the components. [5, 6] The basic operation of core of the operational amplifier, a differential pairs, is as shown in Figure 1 basic differential pair. Differential amplification of the most important as a voltage amplifier, its basic operation can be divided into operating differential mode and common mode operation, the overlap of the differential amplifier characteristics are manifested. As long as the differential amplifier pair coupled with a power amplifier circuit, it will become the operational amplifier of a CMOS element. (1) I SS is current source () when V out 1 = V out, flowing through M 1 and M the bias current is I SS transistor (3) The output common-mode level is V DD R D I SS OPAMP V in1 R D V out1 OPERATION V DD M1 M R D V out V in Figure 1 basic differential pair COMMON-MODE Figure shows a basic differential 3

pair, the differential amplifier to the two input terminal pairs, and received on a common mode signal V in,cm i.e. V out 1 = V out = V in,cm, such as Figure common-mode input differential pair, and the transistor is symmetrical, so obtainedv out 1 = V out. (1) WhenV in,cm = 0, then thei D1 = I D = 0, andv out 1 = V out = 0, the signal is not enlarged. () When V in,cm increases, V out 1 and V out remains fixed, if V in,cm > V out 1 + V TH = V DD R D I SS +V TH,M1 and M will enter triode region. V DD higher, allows the smaller the output amplitude. For this reason, choose low V in,cm is ideal, but the common-mode signals are often from the noise, before a configuration can be easily achieved. OPAMP DIFFERENTIAL-MODE OPERATION Figure shows a basic differential pair, the two inputs of differential amplifier pair, each connected to a different source i.e.v out 1 V out, shown in Figure 3 differential-mode input differential pair. (1) Assumptions R D1 = R D = R D, V out 1 V out = R D I D R D1 I D1 = R D (I D I D1 ) R D V out1 R D V out () Deduced I D1 and I D, and V in,cm M1 M assuming that the circuit is V b M3 Figure common-mode input differential pair symmetrical, and M1 M is located in the saturation region and 0. V DD Broadly speaking, V in,cm of the allowable range values can be the following inequality is limited:v GS 1 + V GS 3 V TH 3 V in,cm min (V DD V in1 R D1 V out1 M1 M X R D V out V in R D I SS + V TH V DD ). When M 1 and M I SS located in the saturated zone, the maximum value of each outputv DD, a minimum value of approximately V in,cm V TH. In other words, the input common mode level Figure 3 differential-mode input differential pair V GS = I D W + V TH μ n C ox L So, the above equation could be arranged 4

to: V in 1 V in = I D 1 μ n C ox W L I D μ n C ox W L Finally, in a series of calculations and obtain: I D1 I D = 1 μ W nc ox L (V in 1 V in ) 4I SS μ n C ox W L (V in 1 V in ) It can be learned from the conclusions of the analysis, ΔI D depends on the ΔV in. When ΔV in increase, ΔI D will increase, due to outside the square of the equation. III. SCHMITT COMPARES THEORY Inverting hysteresis theory V S R i R 1 V ref - + V CC V CC R E sat E sat VTL (a) (b) 0 VTH Figure 4(a) inverting the hysteresis comparator circuit, and 4 (B) conversion characteristic curve Shown in Figure 4(a) inverting the hysteresis comparator circuit, and 4 (B) conversion characteristic curve when V S right, which increased VTH and decreased V TL. When V R 0, V TH and VTL exactly equal positive and negative voltage under symmetrical. And H will not be changed as the reference voltage VR change. V TH = R R 1 + R V R + R 1 R 1 + R E sat V TL = R R 1 + R V R R 1 R 1 + R E sat So: ΔH = V TH V TL = R 1 R 1 + R (E sat ) Positive phase hysteresis theory In Figure 5(a) the relative hysteresis comparator circuit, and 5(b) conversion characteristic curve, which shows that when the comparator for the same phase, then the difference with inverted is as follows: ifv s > V TH,V o = +E sat ; and if V s < V TH, V o = E sat. Those mean V o and V s have the same polarity. V TH = + R 1 E R sat + R 1 + R V R R V TL = R 1 E R sat + R 1 + R V R R Therefore: ΔH = V TH V TL = R 1 R (E sat ) V R 0, VTH and V TL is going to the 5

V CC E sat Figure 7 Schmitt sawtooth wave oscillator V ref R i - + R VTL 0 VTH V S Vcc R 1 V CC V S E sat M10 M11 (a) (b) Figure 5(a) the relative hysteresis comparator circuit, and 5(b) conversion characteristic curve M1 M14 M13 M15 IV. RESULTS AND DISCUSSION M16 M17 output In the research, the design idea of a sawtooth wave generator contains phase hysteresis theory, RC charge and discharge theory, and Schmitt theory, shown in Figure 6 RC charge-discharge and Schmitt positive phase hysteresis circuit. R C V out V CC V ref R 1 R i - + V CC V CC Figure 6 RC charge-discharge and Schmitt positive phase hysteresis circuit 3V DC Vout RT R0 R CT M09 R1 To Opamp Vo To Opamp V+ R To Opamp Vo To Opamp V- Vref Figure 8 Current mirror The principle for the use of the RC charging theory, the current through resistor R continues to charge the capacitor C. When the voltage of the capacitor C is increased from zero to the target value, Schmitt positive phase hysteresis circuit also reachesv TH, i.e. its output V o is changed from low potential to high potential, while the MOS switching fast discharge the capacitor C voltage is zero. After the capacitor C voltage is zero, MOS switch presents an open circuit condition, the RC charge-discharge circuit to start charging. Figure 7 Schmitt sawtooth wave oscillator, wherein the left-most resistor RT, CT RC charging circuit; R, M09, D0 as a RC discharge circuit; R0, R1, and Vref is a Schmitt circuit. Figure 8 Current mirror, by M10, M11, M1, 6

M13, M14, M15, M16, and M17 of the current mirror constituted by the MOSFET. Opamp, The M00, M01, M0, M03, M04, M05, M06, M07, and M08 constitute the operational amplifier, as shown in Figure 9 Opamp. MOSFET switch gate. Vcc M0 M03 V+ To 電電電 M00 M04 M01 Vref M05 M06 M07 M08 Vo Figure 11 internal square wave pattern in sawtooth wave generator HSPICE program.subckt smith Vout vo UV LV VDD GND Figure 9 Opamp Vr V1 GND DC +1.8V R0 Vout 1 50K R1 1 vo 100K R Vout 10 M18 Vout UV VDD VDD pch L=0.35U W=160U CT Vout GND 0.05nF IC=0V D0 vo 7 NDIO M00 4 1 VT GND nch L=0.35U W=10U *G: Opamp V+ Figure 10 the output of sawtooth wave generator Figure 10 the output of sawtooth wave generator in the research, because the RC charge-discharge generated in the time constant is higher, the waveform is slightly saturated. But RC charge and discharge circuit structure is relatively simple, cheaper production costs circuit; there is still the actual benefit. Figure 11 is an internal square wave pattern of the sawtooth wave generator supplied to discharge the M01 5 V1 VT GND nch L=0.35U W=10U *G: Opamp V- M0 4 4 VDD VDD pch L=0.35U W=10U M03 5 4 VDD VDD pch L=0.35U W=10U M04 VT LV GND GND nch L=0.35U W=10U M05 6 5 VDD VDD pch L=0.35U W=55U M06 6 LV GND GND nch L=0.35U W=55U M07 VO 6 VDD VDD pch L=0.35U W=5U M08 VO 6 GND GND nch L=0.35U W=65U M09 7 GND GND nch L=0.35U W=30U.ends.subckt CMirror UV LV VDD GND M10 UV UV VDD VDD pch L=0.35U W=10U M11 9 UV VDD VDD pch L=0.35U W=10U M1 UV 10 11 GND pch L=0.35U W=10U M13 9 10 10 GND pch L=0.35U W=10U 7

M14 11 11 13 GND nch L=0.35U W=10U M15 10 11 LV GND nch L=0.35U W=10U M16 13 LV GND GND nch L=0.35U W=10U M17 LV LV GND GND nch L=0.35U W=10U.ends software and component parameters required resources. And the founding of the University of Science and Technology, Department of Electrical Engineering integrated circuit simulation and design laboratory, provision of computer equipment and technical guidance. Figure 1 IC Circuit layout V. CONCLUSION The Figure 1 IC Circuit layout oriented papers referred to the two kinds of circuit aggregate together the layout, the total area for 1181μm x 107μm. In this thesis, a 0.35-micron process proposed by Taiwan Semiconductor Co., Ltd., the improved design Schmitt sawtooth wave generator has made great improvements in the high voltage saturation phenomenon. Of course, there are still space efforts, pending further research and improvement. VI. ACKNOWLEDGEMENTS The depth to thank the National Chip Implementation Center (CIC, National Chip Implementation Center) to provide free research simulation Reference [1] J. J. Bolder, G. Witvoet, M. R. De Baar, N. Van de Wouw, M. A. M. Haring, E. Westerhof, N. J. Doelman, and M. Steinbuch, "Robust adaptive control of the sawtooth instability in nuclear fusion." pp. 503-508. [] A. Camacho, "On the use of auditory models' elements to enhance a sawtooth waveform inspired pitch estimator on telephone-quality signals." pp. 1080-1085. [3] A. M. Y. M. Ghias, J. Pou, M. Ciobotaru, and V. G. Agelidis, "Voltage balancing strategy for a five-level flying capacitor converter using phase disposition PWM with sawtooth-shaped carriers." pp. 5013-5019. [4] Chang Yi-chu, and Kim Won-Jong, Aquatic Ionic-Polymer-Metal-Composite Insectile Robot With Multi-DOF 8

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