12-10-2016, 03:45 PM
1458827876-DesignofVCOwithharmonicextractioncircuits.docx (Size: 1.12 MB / Downloads: 10)
Abstract- This paper presents a design of LC tank circuit using current mirror that achieves tuning range of 23.17% and Phase noise of -85dBc/Hz with a power consumption of 50uW for a power supply of 5V. The harmonics produced from VCO are extracted by using band pass filter (BPF) and amplified using common gate amplifier and cascode amplifier and differential buffer produces doubler output. The proposed design is simulated using 90nm technology in Cadence Virtuoso Analog Design Environment tool
. INTRODUCTION
VCO’s are used to generate signals of different frequencies by varying the controlled voltage. The low Phase noise and wide tuning range are difficult to obtain for high frequency applications. Push - Push VCOs has been implemented but it produces low amplitude output[1]-[3]. So, Linearisedtransconductance VCO (LITVCO) is used [4][5] but the power dissipation is high in that configuration.In this paper,VCO is implemented using harmonic extraction circuits.Since,the fundamental frequency of VCO is very less,therefore harmonics are extracted that can be used for high frequencyapplications.Harmonics are the integral multiple of fundamental frequency. The harmonic extraction circuits consists of common gate amplifier,cascode amplifier and differential output buffer.[4]
A new technique of VCO has been utilized known as LC VCO with current mirror which improves the VCO phase noise performance , wide tuning range as well as attains low power dissipation.
The paper is organized as follows:Section II explains the design of VCO with harmonic extraction circuits.The harmonic extraction circuits are common gate amplifier, cascade amplifier, differential output buffer and band pass filter (BPF).Section III explains the simulation results and discussions that includes the transient analysis,periodic steady state analysis,phase noise analysis and performance comparison of VCO.Finally section IV is the conclusion of the paper.
II. DESIGN OF VCO
The VCO shown in fig 1 is implemented using harmonic extraction circuits.The harmonic extraction circuits consists of VCO with common gate amplifier,cascode amplifier and differential output buffer.The harmonics generated from VCO are lower in amplitude and having low input impedance.Hence,common gate amplifier is used at the suply end of VCO to increase the bandwith and cascode amplifier is usd at the tail end of VCO to increase the input impedance.Differential output buffer is used to produce doubler output signal which is less sensitive to noise.Band pass filter is used to extract the harmonics produced from VCO.
The LC tank circuit used in this work is a current mirror VCO. The presence of negative resistance in cross coupled configuration compensate all the losses due to the resistance and capacitance but the full potential of LC tank circuit is not utilized and in balanced configuration, large number of components are required to produce a balanced circuit to consume less current.Therefore a new topology is demonstrated in fig 2 where both cross coupled and balanced configuration are used.Both cross coupled and balanced configuration produce better VCO characteristics.Top current control architecture is employed to decrease the system power consumption and phase noise.This VCO architecture will employ two current mirrors which balance the impedance in both the arms of the current mirror circuit and hence current becomes exact replica of the bias current. In case of single current mirror, the impedance is unblanced resulting in different currents in the mirror arms which leads to more power consumption.
CONCLUSION
Current mirror VCO is simulated using CADENCE Virtuoso Analog design environmental tool (ADE). Current mirror VCO is used which attains wide tuning range, lower power dissipation and low phase noise. Transient analysis of different voltages has been determined and corresponding frequency has been measured . Periodic steady state of VCO has been analysed and phase noise of VCO has beencalculated.The performance analysis has shown that the designed VCO has better tuning range,low power and low phase noise which makes it suitable to operate as local oscillator in receiver circuits.