Design and Implementation of High Gain, High Unity Gain Bandwidth, High Slew Rate and Low Power Dissipation CMOS Folded Cascode OTA for Wide Band Applications

Copyright: © 2015 Vadodaria MU, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Design and Implementation of High Gain, High Unity Gain Bandwidth, High Slew Rate and Low Power Dissipation CMOS Folded Cascode OTA for Wide Band Applications


Introduction
Amplifier is one of the basic and important circuits which have a wide range of applications in sever. This is accomplished by the continual integration of complex analog building blocks on a single chip [1]. Gain and Speed both are most important parameter in amplifier. Power dissipation is most important factor in any analog circuit. Designing high-performance base band analog circuits is still a hard task to reduced power consumption and increased frequency and gain [2]. Current tendency focus on some radio-software receivers which suppose a RF signal conversion after the antenna [3]. Thus, a very higher sampling frequency and resolution analog-to-digital converter design is required. Folded Cascode OTA is a solution of Telescopic Cascode OTA. There have some limitations of the voltage swing. To remove the drawback of telescopic OTA i.e. limited output swing and difficulty in shorting the input and output a Folded Cascode OTA is used. This design follows three stages such as (i) Input Pair, (II) Current mirror Cascode Stage and (III) Biasing Stage. Current mirror is a one type of approach to copy current at output side [4].

Design Approach
One way of increasing the impedance is to add some MOSFETs at the output side or in second stage to include for using an active load. MOSFETs are stacked on top of each other. The MOSFETs are called "cascode", and will increase the output impedance and thereby increase the gain [5]. Here in this cascode pair, there is given self biasing using current mirror. The current mirror is one of the main parts of the most analogue and mixed-signal integrated circuits to copy current such as OTAs [5,6].
Here the Figure 1 is consisting of M1 and M2 is called Current Mirror. In the current mirror channel length modulation is neglecting.
So, take ratio of the out I and ref I Constructing the bias circuit of an amplifier to provide the required bias current [7]. Transistor trans-conductance is the most important parameters in amplifier that must be stabilized. In general biasing of an amplifier is to ensure the proper operation of the circuit.

Design Analysis
This schematic design is consisting of three stages. First stage is NMOS input pair, second stage is cascode stage and third stage is biasing circuit. The input stage is designed by N-MOS input pair. Due to the greater mobility of NMOS device, PMOS input differential pair has a lower transconductance than carrier a NMOS pair. Thus, NMOS MOSFET has been chosen to ensure the largest gain required. For a folded OTA bandwidth performance is high. So here N-MOS input pair is applied for high transconductance. So as shown in Figure 2 M1 and M2 are NMOS input pair MOSFETs. be low and its gate terminal is directly connected to the M11, which is work as a PMOS load resistor.    Table 1 presents different sizes of MOSFETs according to its operation. Table 2 represents the summary of proposed performance parameter using 180 nm technology. There are different capacitive load such as 1 pF. 2 pF and 5.6 pF.

Simulation Result
All simulation results are measured by using 180 nm or 0.18_m technology using Mentor Grphics-Pyxis (Figures 3-6).

Conclusion
A novel design of Folded Cascode Operational Transconductance Amplifier (FCOTA) using current mirror as self biasing and biasing of the driving stage has been presented in this research work. The proposed design of FCOTA has been simulated and analyzed using Mentor Graphics tools. Improvement in performance parameters such as Gain up to 97.36 db, UGB up to 20.83 GHz , Reduction in Power Dissipation is 8.31 W and Slew Rate enhanced upto 3.5075 KV/µs has been achieved with respect to reference papers designs. So this FCOTA is designed for low power, high gain and high UGB. And it's used for wide band applications.