Advanced RFIC Design ELEN 359A Lecture 2: Passive Circuits

Instructor: Dr. Allen A Sweet

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Passive Circuit Types

• Low Pass Filters (LPF)• High Pass Filters (HPF)• Band Pass Filters (BPF)• Differential Circuits• Phase Shifters• Splitters/Combiners• Couplers

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Single Section “T” LPF

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Basic Design Equations: Single Section “T” Low Pass Network

• Z0=SQR(L/C)• Fc=1/piZ0C• L=SQ(Z0)C• Time Delay=SQR(LC)• Phase Shift(in degrees)=360F(Time Delay)• Fh=50%Fc• Roll off is about 10 dB per octave per section• Phase shift is about 90 degrees at Fh per section

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Design Example of a Single Section LPF

• Assume Fh=3 GHz, then Fc=6 GHz• Assume Z0=50 Ohms• C=1/pi(50)(6 GHz)=1.06 pF• L=(50)(50)(1.06E-12)=2.65 nH• Time Delay=SQR(2.65E-9)(1.06E-12)=53

ps• Phase Shift=360(3GHz)(53 ps)=57 degrees

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ADS Schematic for a Single Section “T” LPF

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ADS Simulation for a Single Section “T” LPF

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Single Section“T” HPF

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ADS Schematic for a Single Section HPF (Inverting LPF)

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ADS Simulation of a Single Section “T” HPF

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ADS Schematic of a Two Section LPF using Spiral Inductors

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ADS Simulation of a Two Section LPF with Spiral Inductor

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ADS Schematic for a Two Section HPF using Spiral Ind

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ADS Simulation of a Two Section HPF with Spiral Ind

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Basic Differential Circuit Topology

50 Ohm

50 Ohm

0 Degrees

180 Degrees

Virtual Ground

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ADS Center Tapped Transformer Element TF3

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Transformer Phase Splitter

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Simulation of Transformer phase Splitter

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ADS Schematic of a Single Section Differential LPF

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ADS Simulation of a Single Section Differential LPF

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Band Pass Filter Types

• Cascade an LPF and a HPF• Use a series or parallel resonant LC circuit

per section. Couple with series capacitors.• Use ½ wavelength microstrip resonator

sections. These filters are very large for IC applications, except at very high frequency.

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ADS Schematic of a Cascaded LPF and HPF forming a BPF

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ADS Simulation of a BPF Formed by Cascading LPF, HPF

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ADS Schematic of a Two Section Parallel Resonant LC BPF

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ADS Simulation of Two Section Parallel Resonant LC BPF

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ADS Schematic of a Microstrip ½ Wavelength Resonator BPF

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ADS Simulation of a ½ Wavelength Microstrip

Resonator BPF

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Splitters, Combiners, and Couplers

• Wilkinson 3 dB Power Splitter/Combiner• Resistive 6 dB Power Splitter/Combiner• High Ratio Directional Coupler

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¼ Wavelength Wilkinson 3 dB Power Splitter/Coupler Schemati

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Simulations of Wilkinson 3 dB Power Splitter/Combiner

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Schematic of a Wilkinson 3 dB Splitter Using Spiral Inductors

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Simulations of a Wilkinson Splitter/Coupler using Spiral Ind

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Schematic of a 6 dB Resistive Power Splitter/Combiner

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Simulations of a 6 dB Resistive Power Splitter/Combiner

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Schematic of a ¼ Wavelength Microstrip High Ratio Coupler

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Simulations of a ¼ Wavelength Microstrip High Ratio Coupler

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Homework #1: Differential BPF Design

• In Band Insertion loss < 1.0 dB• In Band Input/output match<-10 dB• Bandwidth: 5.20 GHz to 5.90 GHz (802.11a)• Reject Bands: 2.0 GHz to 2.5 GHz and 10.0 GHz

to 12.0 GHz• Rejection > 30 dB• Schematic to include all layout elements (I.e.

Spiral inductors) and any anticipated layout parasitics.

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