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This paper presents a design of the transimpedance amplifier using 0.35µm CMOS technology. In the proposed transimpedance amplifier, feedback resistor R F of conventional transimpedance amplifier has been replaced by NMOS transistor as an active feedback resistor. This circuit operates at 3.3V power supply voltage and for a photocurrent of 0.5µA.The proposed transimpedance amplifier having low noise, high gain and large dynamic range. KeywordsTransimpedance amplifier, CMOS technology, low noise amplifier, optical receive, negative feedback. INTRODUCTONA transimpedance amplifier (TIA) is a circuit that converts a current signal into output voltage signal whose voltage is dependent on magnitude of current. The demand of higher data rates transportation over the internet and multimedia communication in recent years result in fast development of high speed optical communication system. Transimpedance amplifiers are very useful circuit components in optical communication system. Front-end of transimpedance amplifier (TIA) is one of most critical building block at electro optical interface on receiver side, which determines the performance of whole system to a large extent, such as speed, gain, sensitivity and noise etc. The performance of optical interconnection system depends on receiver gain, bandwidth, noise and power consumption. Silicon-based CMOS technology [1] is the only candidate which can achieve the required level of integration with reasonable speed, gain, cost, power consumption. The transimpedance amplifier [2] uses a closed loop circuits as shown in figure 1. This circuit allows not only to avoid the problem of the dynamic range, but also to obtain a trade-off between the high and low impedance configuration. It is relatively high bandwidth and dynamic range as well as a good noise level. Figure 2 shows CMOS transimpedance amplifier circuit used a push-pull inverter at the input to maximize the transconduction of amplifier [4] and increases its gain bandwidth product (GBP). CIRCUIT DISCRIPTION Figure 2: CMOS transimpedance amplifierThe transimpedance amplifier takes a current from input and converts it into a voltage signal. The transistor T1 and T3 from the inverter while T2 is added to increases the bandwidth and minimize the miller effect.

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Use of spatial phase measurement techniques in a displacement-measuring grating interferometer using detector width compensation becomes impractical due to the highly sensitive nature of the phase spectrum at the wrapped edges (−π and π) to the noise in the system. A usual unwrapping mechanism to accumulate phase fails to avoid any false jump of phase cycle near these edges and results in unwanted errors in displacement data. A new way of using such algorithms is proposed, which avoids these edges during accumulation of phase and hence reduces errors in displacement measurements. A conventional 90 • phase step, four-point algorithm can be used simultaneously with a modified three-point phase algorithm, which gives a similar phase incremental value except the difference in instantaneous phase value. We have implemented this shift in origin to avoid the wrapped edges and have used a sequence of incremental phase values to generate cumulative phase and therefore displacement data by simultaneously using both algorithms in our detector-width-compensated displacement-measuring grating interferometer. Simulation results are introduced to show the usefulness and accuracy of this approach compared to a conventional phase unwrapping mechanism.