The Front-End Receiver's High Precision Voltage Mode Band Gap Reference Circuit

10 | P a g e DOI: 10.5281/zenodo.17358606 The Front-End Receiver's High Precision Voltage Mode Band Gap Reference Circuit Mr. S. Mohan Das Research Scholar, Electronics and Communication Engineering, YSR Engineering College of Yogivemana University Korrapadu Road, Proddatur, Ysr District, Andhra Pradesh Dr Kota Venkata Ramanaiah Professor, Electronics and Communication Engineering YSR Engineering College of Yogivemana University Korrapadu Road, Proddatur, Ysr District, Andhra Pradesh Abstract An essential component of analog integrated circuits' reference voltage generation is the bandgap reference circuit (BGR). The power supply rejection ratio (PSRR), which is utilized to keep the output steady during the transient response, is typically used to represent BGR. Although the BGR circuit is used by receiver front-end transceivers, the system's challenges are thought to be its high-power requirements, sensitivity, complex design, and dynamic range. In order to address the challenges in the system, the Bipolar Junction Transistor (BJT) is added to the Proportional to Absolute Temperature (PTAT) generator cell in order to attain a high factor. In particular, the temperature coefficient (TC) is adjusted for by mutually compensating the first and second-order temperature dependency factors𝑽𝑹𝑬𝑭. By adding bipolar transistors, the length of the transistors is utilized to reduce power consumption and limit the impacts of manufacturing variation and mismatches. The starter circuit, Complementary to Absolute Temperature (CTAT), and PTAT generator cell, which sustains the steady output even in the face of transient response, make up the BGR circuit. The region of 1.2V is where the greatest reference voltage was reached. Keywords— Bandgap reference circuit, Receiver front-end transceivers, Reference voltage, generator cell, Temperature coefficients. I. INTRODUCTION By eliminating surface acoustic wave (SAW) filters, the contemporary radio frequency (RF) front end lowers overall costs [1] [2] [3] [4] [5] [6]. However, because there aren't any high Q filters, the RF front end needs a wide dynamic range. The signal and local oscillator pathways with high power consumption meet strict standards. In order to raise the compression point, current mode techniques restrict the strength in the signal channel. The widespread use of voltage mode circuits in RF transceivers draws attention to their effective compatibility and scaling features [7]. The amplifier is regarded as the essential part of the receiver front-end transceiver, and an electromagnetic radar system is employed for object identification and detection [8] [9] [10]. The low noise 11 | P a g e DOI: 10.5281/zenodo.17358606 amplifier (LNA) effectively processes both strong and weak echoes of the incoming signal. The LNA enhanced the signal-to-noise ratio and high gain when the signal was weak. Because LNA operates at a low gain for shortrange objects and has strong linearity and dynamic range, it is possible to prevent receiver chain saturation [11]. High-frequency distortion is compensated for using UPFC circuits, which are utilized in power injection. The UPFC circuits are made up of injection transformers, series VSC, DC link, and shunt voltage source converters (VSC). [12] [13]. Matrix converters take the place of the DC link in direct AC-AC connections [14] [15] [16]. However, the big installation, losses, and limited dynamic responsiveness were the main problems created by the bulky series injection transformer [17][18][19]. Magnetic loss and parasitic resonance cause narrow frequency ranges. [20] [21]. resistive divider and AC-DC converter to create an adaptive biasing (ADB) network. The ohmic operation of a junction field effect transistor (JFET) is achieved by the employment of resistors. Using the DC load signal from the rectifier, the JFET manipulates the corresponding resistor in the ohmic region [11]. The low-dropout regulator (LDO) is dependent on the reference voltage, which is produced by the CTAT block in analog devices [22]. The ripple voltage of BGRs affects the accuracy of the LDO's output. The BGR approach optimizes the ripple rejection capabilities, and voltage reference accuracy is crucial for the overall functioning of the circuit. When determining the range of the pulse signals in the Ultra-wide Band (UWB) system, the accuracy of the system is influenced by the RF transceiver's front-end bandwidth (BW). UWB systems have higher requirements for positioning accuracy and communication distance. High sensitivity, transmitting power, and dynamic range are required for both sending and receiving routes. The intricacy of the bias and control circuits in the transceiver front end design makes integration more challenging [23]. Multiple RF frontends raise the BW of the entire channel, increasing system cost and power usage [24]. The direct sampling receivers (DSR) prevent analog mixing problems such as reciprocal mixing [25], harmonic down-conversion [26], and picture concerns [27]. However, to lessen the problems with noise folding and aliasing, tunable RF filters are needed [28] [29]. The filter must loosen the jitter requirements because the sample pulses are generated by the Phase-locked Loop (PLL) [30] [31]. The multi-transistor used in adaptive biasing circuits takes up a lot of space, and the circuits' low precision and intricate design are regarded as drawbacks. Although the complexity structure is unsuitable for deploying the discrete circuits, the gain is adjusted using a Gillbert-cell-based topology [11]. The PTAT generator cells in this study are connected in series to add up the distinct currents and voltages. The voltage reference temperature is compensated by temperature dependency of the first and second orders. Lastly, to attain a high 𝐾𝐼factor, BJT is added to the PTAT generating cell. The CTAT temperature dependence 𝑉𝐶𝑇𝐴𝑇is matched by increasing the PTAT temperature dependence term 𝑉𝑃𝑇𝐴𝑇due to the transistor layer. By adding the BJT, the transistors' length is utilized to limit the effects of production variations and mismatches, which in turn lowers power consumption. The design of the BGR circuit with a single BJT branch to achieve the stable reference voltage is the primary contribution of the study. II. LITERATURE SURVEY The literature review section discusses current approaches and their drawbacks. The CMOS BGR circuit, created by Trang Hoang et al. [7], was utilized to maximize the PSRR, a measure of the circuit's capacity to sustain a steady 12 | P a g e DOI: 10.5281/zenodo.17358606 output. The algorithms maximized the differential gain to maximize the PSRR, and current source blocks were used to improve the bias accuracy. To keep the rotational angular speed constant, weight parameters were used. To reach the PSRR value, the TC parameter must, however, surpass its limitations. Haishi Wang et al. [24] introduced the mixer-first receiver, which uses baseband noise elimination to lower power. The wide bandwidth and filtering profile were made possible through the manipulation of pole and zeros locations using capacitive feedback. Analog receiver performance for high-data transmission at low and high power levels. However, because of the infinite bands, the noise cancellation technique offered ineffective pulse transmission. The improved beta multiplier was incorporated into the bandgap reference circuit, which was introduced by R. Nagulapalli et al. [33]. The NMOS transistors' fixed resistors were moved, and PMOS transistors reduced the mismatch. Utilizing the reference circuits, which take up less space, decreased power consumption. Large body effects, however, caused mistakes in CMOS technologies. Using the lower power components, Mowei Lu et al. [21] created the power flow and quality control structure. The power supply was supplied via shunt and series converters with high-frequency interconnections, and the ground connections were avoided by using floating modules. In order to achieve the high power and frequency, compact size, and volume, bulky and dynamic line transformers were not used. However, in meshed grids, the power flow control method is the primary cause of unregulated power flow, which results in overload problems. III. MOTIVATION The BGR circuits are essential for producing the reference voltage (VR) in analog integrated circuits. The PSRR, which sustains a steady production, determines BGR ability. The overall performance of the circuit was impacted by variations in the supply. However, the power electronics devices' accurate current sensing enhances the protection, control, and reliability mechanisms. Because of the limited device storage in wide band gap semiconductors, the current sensing approach makes monitoring the different currents more difficult. Therefore, in order to offer a consistent reference output voltage, the BGR circuit design needs to be changed. IV. CHALLENGES This section examines a number of issues with the current approaches that the suggested Bandgap reference circuit resolves. • The feedback loop's stability is guaranteed by a multistage amplifier, which calls for big capacitors and bias currents for compensatory purposes [2]. By ignoring the high-order effects, equation-based approaches decreased the efficacy of analog circuit design [7]. • The second stage circuit had to compensate for the high-frequency gain since the cascade circuit in the c-band receiver circuit integration was more sensitive. The receiver circuit's out-of-band suppression was improperly constructed. [23]. • To achieve the huge gain, a large miller capacitance was needed, and differential signalling was needed at the Transimpedance Amplifier (TIA) to lessen the impact of common mode noise [32]. 13 | P a g e DOI: 10.5281/zenodo.17358606 V. SYSTEM MODEL OF BANDGAP REFERENCE CIRCUIT The semiconductor bandgap, which takes into account the particular circumstances to provide a stable output voltage at a certain value, is proportional to the bandgap VR. The temperature affects the semiconductor's physical characteristics, hence it also affects the output voltage. The modest temperature dependency of charge mobility carriers in Si semiconductors leads to the adoption of bandgap voltage reference circuits. A three-terminal device called the BGR circuit is used to lessen variations in potential differences. In BGR circuits that are nonlinear, a high supply voltage causes a slight variation in VR. The BGR voltage source is designed using two elements with distinct TCs. Transistors, op-amps, and/or diodes make up BGR circuits. The BGR circuit is made up of current mirrors and a steady current source. The current mirror uses two PNP transistors to control the current. The output VR is provided by two transistors that are positioned at the bottom. The VR and the voltage drop between the transistor Q2 and resistor are same. When the base-emitter current flows via a forward-biased diode, the transistor travels linearly, and the overall voltage drop in this area is proportional to the bandgap. In the BGR circuit, the resistor has a positive TC and the transistor has a negative TC. When selecting the opposing TCs of the components, the resulting VR has 0 TC. Figure 1 illustrates the system model of the BGR circuit. Figure 1 Bandgap Reference Circuit System model. A. Proposed Bandgap Voltage reference using single Bipolar Junction Transistor Branch Each transistor in the bandgap voltage reference circuit has a threshold voltage level above 0.6 V, which is utilized to activate the gate-source voltage. The starter circuit receives a reference current. Low leakage current aids in fully shutting off the startup circuit during CR (Current reference) operation. The trimming circuit is added to the CTAT circuit to offset the mismatch effects caused by the PTAT Slope if the circuit rises above the threshold level. Startup problems are lessened since a large percentage of PTAT cell transistors are grounded. By adding BJT transistors at the last layer of the circuit design, the power consumption is decreased and the temperature dependency coefficients are increased. Transistors' length is utilized to reduce the effects of process variation. At various stages of the operation, the BJT transistor's base-emitter voltage is less impacted. To account for the TCs, temperature dependency terms of the first and second orders are employed. The second-order effect of 𝑉𝐶𝑇𝐴𝑇 and 𝑉𝑃𝑇𝐴𝑇 optimizes TCs. 14 | P a g e DOI: 10.5281/zenodo.17358606 Figure 2. Block schematic of suggested Bandgap Reference Circuit B. Architecture of Bandgap Reference circuit Figure 3. Bandgap Reference circuit Architecture By preserving symmetry, the BGR layout configuration uses the least amount of space possible, preventing mistakes and inconsistencies. The layout design makes use of smaller, interconnected component units. The bandgap reference circuit's area is. Each component's layout is created using the Layout vs. Schematic (LVS) and Design Rule Checking (DRC) guidelines. By filling the gaps between the components, the decoupling capacitors (DECAPs) in this arrangement help to lower circuit noise. DECAPs are made with NMOS transistors, while PMOS transistors are employed for low leakage applications. The ground is connected to the NMOS transistors that round the guard ring. The supply voltage, which polarizes the transistor bodies, is coupled to guard rings. The BGR circuit architecture of the RF frontend transceiver is shown in Figure 3. C. Startup circuit Low voltage CR is used in the startup circuit to lower power consumption, and the biasing circuit is necessary for the transistors to function in the sub-threshold area. 2𝑛𝐴 is the range of the reference current value. Each transistor in the startup circuit region activates the gate-source voltage to fully start the circuit when 𝑉𝑇𝐻 >0.6𝑉. Additionally, the starter circuit in the CR operation is turned off using the low leakage current. PMOS and NMOS transistors are used in the starter circuit to convert the zero current area into a typical working zone. The BGR circuit's regular behavior is altered in the herbinate mode by using every transistor in the starting circuit. D. Complementary to absolute Temperature voltage. The circuit's PNP transistor Q1 is designed to produce the base-emitter voltage needed to determine the circuit's CTAT voltage. The circuit's voltage divider is attached to transistor Q1. The 𝑽𝑪𝑻𝑨𝑻 is produced by converting the high voltage into a tiny voltage in accordance with the voltage rule. One way to write the mathematical expression is, 15 | P a g e DOI: 10.5281/zenodo.17358606 𝑉𝐶𝑇𝐴𝑇 =𝑉𝐵𝐸 3 (1) where 𝑉𝐵𝐸 is the PNP transistor's base-emitter voltage. To mitigate the effects of the load, a unity gain buffer is added to the divider, using the 2nA current range. The capacitance is added to the buffer to keep it stable. To account for the temperature, the 𝑉𝐶𝑇𝐴𝑇 can be used to compute the first and second order temperature dependent terms. The resulting mathematical formula is as follows: 𝜕𝑉𝐶𝑇𝐴𝑇 𝜕𝑡 =𝑉𝑏𝑒 −𝑉𝐵𝐺𝑅 −𝛽𝑉𝑡 3𝑡 (2) 𝜕2𝑉𝐶𝑇𝐴𝑇 𝜕𝑡 =1 3(1 𝑡𝜕𝑉𝑏𝑒 𝜕𝑡 −𝑉𝑏𝑒 𝑡2) (3) where 𝑉𝐵𝐺𝑅 is the bandgap VR and ′𝑡′ is denoted as the temperature. The collector current is used to modify the temperature dependence of the CTAT. E. Trimming circuit To address the output fluctuation in the various corners, the circuit design incorporates a trimming circuit. Implementing the trimming circuits fixes the process fluctuations and device mismatch circumstances that reduce output voltage accuracy. By modifying the aspect ratio 𝑘𝑎, the trimming circuits are utilized to maximize the TC. The trimming circuit's design can be represented as follows: Figure 4. Schematic of Trimming circuit. The trimmer circuit modifies the PTAT slope to maximize TC by combining four transistors and four switches in series. For each sample in the VR measurement, the mean of TC is lowered in the trimmer circuit. The TC of the output current and voltage determines how the supply voltage varies. Figure 4 shows a representation of the trimming circuit. VI. RESULTS AND DISCUSSIONS Effective post-layout and pre-layout findings are provided in this results and discussion section to demonstrate the circuit's effectiveness. A. Experimental setup To implement the BGR circuit, the PSpice/LT Spice platform is utilized. LTspice software's analog electronic circuit simulator is utilized in linear technology, analog device, and maximum integrated source models. In order to save time and money, complicated equipment designs are created by simulating complex mixed-signal systems using PSpice software. 16 | P a g e DOI: 10.5281/zenodo.17358606 B. Post layout results The system's post-layout outcomes are derived from the simulations, and the layouts are extracted from the simulations using DRC and LVS. 1. Startup voltage The output voltage of 𝑉𝐶𝑇𝐴𝑇 generation is determined by the BGR circuit's startup time. According to Figure 5, the supply voltage stays steady at 3.3V between 200 and 500 μs by increasing linearly from 100 μs. Meanwhile, the voltage is generated by the V_CTAT at 130 μs, and it climbs linearly to 200 μs afterwards. In the region of 1.2 V, the 𝑉𝐶𝑇𝐴𝑇 keeps the bandgap VR steady at 200μs. From 200 to 500 μs, this voltage keeps the output steady. Figure 5 shows the voltage upon starting. Figure 5(a). Characteristics of Startup voltage 2. Bandgap VR Figure 5(b). Characteristics of reference voltage In order to create the VR, Bandgap VR balances the positive and negative TC. Temperature is taken into account in the post-layout simulation results between -40°C and 120°C, and the VR reaches its maximum voltage at these temperatures. When the temperature was -40°C, the VR reached 1.1949V. At a temperature of 40°C, 1.9676V is reached, which is regarded as the highest VR level. Following that, the VR drops linearly with less fluctuation between 600 and 1200C. Figure 6a shows the bandgap VR waveform, and Figure 6b shows the bandgap VR in the corners. 17 | P a g e DOI: 10.5281/zenodo.17358606 Figure 6. a) Bandgap VR, b) Bandgap VR in corners 3. Supply frequency Vs temperature sweep The components that create the VR dependent on temperature are PTAT and CTAT. In the BGR circuit, raising the temperature causes the PTAT voltage to rise and the CTAT voltage to fall. To cancel the change in voltage drop, these components are connected in series and their settings are adjusted. Regarding the temperature range of -400 C to 1200 C, VCTAT in the BGR circuit drops linearly from 0.81 V to 0.50 V. Furthermore, depending on the temperature range of -400 C to 1200 C, the VPTAT grows linearly from the 0.39V to 0.70V range. The bandgap VR of 1.20V is obtained by adding these two values. The link between temperature sweep and supply frequency is shown in Figure 7. Figure 7. Temperature sweep Vs Supply frequency 4. Temperature dependence of voltage In CTAT circuits, the output voltage has an inverse relationship with the negative TC. The output voltage of the CTAT decreases between 60 and -25V as the temperature rises. The Vref was designed using the temperature dependence VCTAT, which is depicted in Figure 8. As the threshold voltage changes more, the temperature dependency of VCTAT reaches negative voltage. Regarding the temperature range of -40°C to 120°C, the voltage fluctuates between 60V and -25V. In the temperature range of 420C, the temperature dependency of VCTAT reaches 0V. The voltage's temperature relationship is seen in Figure 8. 18 | P a g e DOI: 10.5281/zenodo.17358606 Figure 8. Characteristics of Temperature dependence of voltage 5. Supply voltage Vs sweep voltage Depending on the source voltage, the voltage sweep signal increases linearly from minimum to maximum. With respect to the 2V sweep voltage, the bandgap VR reaches 1.11V. In relation to the sweep voltage range of 2.2V to 4V, the VR increases linearly from 1.15V to 1.22V. Figure 9 illustrates the connection between the supply voltage and sweep voltage. Figure 9. Characteristics of Supply voltage Vs sweep voltage 6. Temperature Dependence of Proportional Absolute Temperature Voltage The derivative calculus, which is used to examine the rate at which electrical quantities in a circuit change, was used to study the voltage and power behaviors in the BGR circuit. The derivatives are utilized to comprehend the circuits' stability and transients. The temperature-based derivative of the PTAT voltage is calculated. Regarding the sweep voltage, the VR linearly drops from the 350–180 mV range in the temperature dependence VPTAT. After that, the VR keeps the output range of 48 V steady with respect to the sweep voltage. The temperature dependence VPTAT is displayed in Figure 10. The amplifier circuit analyzes power values using derivatives, which enhances the circuit's dynamic behavior and maximizes performance. Figure 10. Characteristics of Temperature dependence of VPTAT