Comparative Analysis of two stage High gain opamp

A High Swing Ultra-Low-Power Two Stage CMOS OP-AMP in 180 nm and 350nm Technology with 1.5V supply, is presented. Cascode technique has been used to increase the dc gain. The unity-gain bandwidth is also enhanced using a gain-stage in the Miller capacitor feedback path. It have 92.45 degree phase margin. The circuit has 94.866dB gain for 180nm. The power dissipation of the designed only is approximately 45uw, and correspondingly gain for 350nm is 85.43db. The designed system demonstrates relatively suitable response in different temperature. (1)Introduction Operational Amplifiers (Op amps) are one of the most widely used building blocks for analog and mixed-signal systems. They are employed from dc bias applications to high speed amplifiers and filters. General purpose op amps can be used as buffers, summers, integrators, differentiators, comparators, negative impedance converters, and many other applications. With the quick improvements of computer aided design (CAD) tools, advancements of semiconductor modeling, steady miniaturization of transistor scaling, and the progress of fabrication processes, the integrated circuit market is growing rapidly. Nowadays, complementary metal-oxide semiconductor (CMOS) technology has become dominant over bipolar technology for analog circuit design in a mixedsignal system due to the industry trend of applying standard process technologies to implement both analog circuits and digital circuits on the same chip. While many digital circuits can be adapted to a smaller device level with a smaller power supply, most existing analog circuitry requires considerable change or even a redesign to accomplish the same feat. With transistor length being scaled down to a few tens of nanometers, analog circuits are becoming increasingly more difficult to improve upon. The operational amplifier is one of the most useful and important components of analog electronics. They are widely used in popular electronics. Their primary limitation is that they are not especially fast: The typical performance degrades rapidly for frequencies greater than about 1 MHz, although some models are designed specifically to handle higher frequencies. The primary use of op-amps in amplifier and related circuits is closely connected to the Concept of negative feedback. Feedback represents a vast and interesting topic in itself. We will discuss it in rudimentary terms a bit later. However, it is possible to get a feeling for the two primary types of amplifier circuits, inverting and non-inverting, by simply postulating a few simple rules (the \golden rules"). We will start in this way, and then go back to understand their origin in terms of feedback. (2)Basic Block diagram CMOS op-amp Operational Amplifiers are the backbone for many analog circuit designs. Op-Amps are one of the basic and important circuits which have a wide application in several analog circuits such as switched capacitor filters, algorithmic, pipelined and sigma delta A/D converter, sample and hold amplifier etc. The speed and accuracy of these circuits depends on the bandwidth and DC gain of the Op-amp. Larger the bandwidth and gain, higher the speed and accuracy of the amplifier Op-amp are a critical element in analog sampled data circuit, such as SC filters, modulators. The general block diagram of an op-amp with an output buffer is shown below Figure 1. Block diagram of Op-Amp The first block is a differential amplifier. It has two inputs which are the inverting and noninverting voltage. It provides at the output a differential voltage or a differential current that, essentially, depends on the differential input only. The next block is a differential to single-ended converter. It is used to transform the differential signal generated by the first block into a single ended version. Some architecture doesn’t require the differential to single ended function; therefore the block can be excluded. In most cases the gain provided by the input stages is not sufficient and additional amplification is required. This is provided by intermediate stage, which is another differential amplifier, driven by the output of the first stage. As Vikas Sharma, Anshul jain / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 2, March -April 2013, pp.1802-1804 1803 | P a g e this stage uses differential input unbalanced output differential amplifier, so it provide required extra gain. The bias circuit is provided to establish the proper operating point for each transistor in its saturation region. Finally, we have the output buffer stage. It provides the low output impedance and larger output current needed to drive the load of opamp or improves the slew rate of the op –amp. Even the output stage can be dropped: many integrated applications do not need low output impedance; moreover, the slew rate permitted by the gain stage can be sufficient for the application. If the op-amp is intended to drive a small purely capacitive load, which is the case in many switched capacitor or data conversion applications, the output buffer is not used. When the output stage is not used the circuit, it is an operational transconductance amplifier, OTA. The purpose of the compensation circuit is lower the gain at high frequencies and to maintain stability when negative feedback is applied to the op