LC-Tank Colpitts Injection-Locked Frequency Divider With Record Locking Range

S.-L. Jang, Senior Member, IEEE, S.-H. Huang, C.-F. Lee, and M.-H. Juang, Senior Member, IEEE

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Presenter: 楊 子 岳

Abstract

• The ILFD is based on a VCO with two embedded injection MOSFETs for coupling external signal to the resonators.

• The new VCO is composed of two single-ended VCOs coupled with cross-coupled MOSFETs and a transformer.

• Supply voltage of 1.5 V, free-running frequency is tunable from 5.85 to 6.17 GHz.

• Incident power of 0 dBm the locking range is about 7.1 GHz (65.4%) from the incident frequency 7.3 to 14.4 GHz.

• The ILFD has a record locking range percentage among published divide-by-2 LC-tank ILFDs.

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Outline

• Introduction• Circuit Design• Measurement Results• Conclusion

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Introduction

• The main concern for the frequency divider design is large locking range with low power consumption.

• For high speed and low power operation LC-tank ILFD is the most suitable one among various types of frequency dividers because operating frequency is determined by the resonant frequency.

• The ILFD is based on a new VCO topology and two injection MOSFETs for coupling external injection signal to lock the VCO output signal.

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Circuit Design

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• Schematic of a single-ended VCO and its equivalent LC resonator

•Transistors (M5,M6) are configured to provide negative resistance Rin to compensate for the tank loss.•The VCO provides two unbalancedoutputs from the terminals of inductor L2 . The varactors are used to tune VCO output frequency.

Circuit Design

k is the coupling coefficient 6

• Schematic of the proposed ILFD The cross-coupled transistors are used to couple the two single-ended VCOs to form a differential VCO and also provide a net negative resistance to the VCO to compensatefor the loss due to the resistance in inductors, varactors, and injection MOSFETs.

L1,L2 are used to couple differentially the two single-ended VCOs.

Circuit Design

• To obtain a wide-locking range:1) firstly appropriately choosing the location of injection

MOSFET is important, because the location affects the efficiency of injection.

2) Secondly, the size of Min is optimized, as the channel width W of Min is increased , the resonator Q-factor is degraded and the voltage swing of ILFD output decreases, these lead to the increase in locking range, however if W is too large, the ILFD can not oscillate because two output ports of inductor are shorted.

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Circuit Design

• Simulated

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Fig. 2. Simulated ac input gate voltage (bottom plot) of M and ac output voltages (top plots) of the buffers at injection-locked condition

Measurement Results

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Fig. 4. Measured free-running frequency tuning range of the ILFD circuit.

•tunable from 5.85 to 6.17 GHz with a tuning voltage from 0 to 1.5 V when dc bias voltage Vinj is 1.5 V

Measurement Results

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Fig. 5. Measured and simulated relationship between input sensitivity and operating frequency at the supply voltage of 1.5 V

At 1.5 V, a signal power of 0 dBm provides a locking range of 7.1 GHz, from 7.3 to 14.4 GHz

Measurement Results

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Fig. 6. Measured phase noises of the free-running, injection-locked and injection-reference. Injection power = 0 dBm, f = 6.13 GHz.

The phase noise of free-running oscillator at 1 MHz offset is about 104.5 dBc/Hz. After external power injection,the phase noise of ILFD is about 134.8 dBc/Hz

Conclusion

• A new LC oscillator based ILFD has been proposed and fabricated in TSMC 0.18 um CMOS technology.

• It consists of two single-ended Colpitts VCOs coupled with cross-coupled MOSFETs and transformer to form a differential circuit.

• The free-running frequency operates from 5.85 to 6.17 GHz at the supply voltage of 1.5 V and power consumption of 7.65 mW. The locking range is from 7.3 to 14.4 GHz which is up to 65.4% when input power is 0 dBm.

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Thanks for your attention

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