Advanced RFIC Design ELEN359A, Lecture 3: Gilbert

Cell MixersInstructor: Dr. Allen A Sweet

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All of Design is the Art and Science of Navigating Tradeoffs

• Science gives us the tools to understand what nature, in the form of the laws of physics, will allow us to do and not to do.

• Tradeoffs are the points where we as designers must make decisions.

• The Art of design is the process by which we make good decisions given numerous factors such as economics, market acceptance, cost of development, competitive pressures, etc.

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Basic Non Linear Process Produces Mixer Action

• Active Device Non Linearity is Expressed as a Power Series relating the device’s Voltage and Current: I(t) = I0 + k1V + k2V*2 + k3V*3 + …

• If V = V1 + V2 (two input signals), the second order term becomes: k2(V1*2 + V1V2 + V2*2). It is the V1V2 product term that produces mixing action because if V1 and V2 are sin waves, their produce, (v1cosW1t)x(v2cosW2t) = (v1v2/2)[cos(W1-W2)t + cos(W1+W2)t] contain the sum and difference mixing Frequencies.

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Down Converting Mixer: Applications to Receivers

FI=Fl-Fr

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Up Converting Mixer: Applications To Transmitters

FR=Fl+/-FIUSBLSB

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Double Balanced Diode Mixer Topology

L VirtualGround

R VirtualGround

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Diode IV Characteristics

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VBIC Diode IV

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ADS Schematic of a Balanced 4 Diode Mixer

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HB Controller, Gain Equation and RF Source

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LO Source

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HB Controller

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HB Controller to Sweep RF_pwr

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Conversion Loss vs RF_pwr

Gain CompressionBegins

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HB Controller to Sweep LO_pwr

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HB Controller to Sweep LO_pwr

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Conversion Loss vs LO_pwr

(LO Amp Requires100 mA Current @30 % efficiency)

(Preamp Requires20 mA Current to Boost Gain to +10 dB)

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Single Balance Bipolar Transistor Multiplying Mixer Topology

Vi = Vl x Vr

Q1 collector currentControls Transconductance

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Advantages of a Single Balanced Bipolar Transistor Multiplier

• High Conversion Gain (5 to 10 dB)• High L to R Isolation (but not high L to I

Isolation).• Low LO power Requirement (-10 to 0

dBm).• IIP3 is higher than the LO power level. • Low DC Power, Small size

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Double Balanced (Gilbert Cell) Bipolar Transistor Mixer

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Advantages of a Gilbert Cell Transistor Mixer

• All Three ports are differential, which is a natural configuration for creating Quadrature Phase Modulators and Detectors.

• L to R, L to I Isolations are excellent. • All the Advantages of the Single Balanced

Transistor Mixer are available in this case.

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A Direct Conversion Receiver using Gilbert Cell Mixers

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Gilbert Cell Mixer Topology

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Fully Differential Mixer Cell

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Series Diode Bias Tree

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DC Power and Output Term

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RF and LO Sources

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HB Controller and Equations

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Harmonic Balance Controller

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DC Analysis

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Bias Tree DC Levels

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MIX Function Determines Frequency Index

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Basic Simulation Calculates Conversion Gain in Two Ways

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LPF Eliminates Spurious Signals in the Mixer’s Output

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Mixer Simulation including an Output LPF.

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HB Controller to Sweep LO_pwr

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HB Controller to Sweep LO_pwr

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Simulation of Gain vs LO_pwr

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HB Controller for Sweeping RF_pwr

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HB Controller to Sweep RF_pwr

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Simulated Gain vs RF_pwr

(P-1dB)

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S Parameter Controller Simulates Isolations and Matches

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Matches and Isolations of a Gilbert Cell Mixer

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Disabling one Transistor Creates Imbalance and Poor Isolation

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Gilbert Cell Up Converter

(i.e. F2+/-F1)

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Up Converting Mixer HB Controller and Equations

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Sources for Up Converting Mixer

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BPF Selects a USB or an LSB Output

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Up Converter Simulation Including MIX Function Table

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USB Output is Selected with the BPF

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HB Controller and Equations to Simulate OIP3

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LO and RF Sources for Intermodulation Simulations

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HB Controller-Freq

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HB Controller-Sweep

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HB Controller- Solver

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HB Controller- Params

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MIX Function Determines Frequency Index for each Signal

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Intermodulation Spectrum

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Gain and OIP3(upper and lower) vs LO_pwr

(dBm)

(dB)

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LO and RF Sources to Simulate Non Linear Noise Figure

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HB Controller and Equations for Noise Figure Simulation

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HB Controller-Freq

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HB Controller-Params

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HB Controller- Noise(1)

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HB Controller-Noise (2)

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HB Controller-Solver

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HB Controller- Output

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Simulated ssb Noise Figure

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Simulated Noise Figure (dsb) and Conv Gain

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Noise Voltage Output at 400 MHz in a 1 Hz Bandwidth

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Home Work #2:A Down Converting Mixer for Wi-Fi

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• Design a Down Converting Gilbert Cell Mixer for 802.11B (RF_freq=2400 MHz). This mixer will down convert received Wi-Fi signals to an IF frequency of 850 MHz where a cellular/PCS receiver will process them. Conversion gain is to be at least 10 dB. As part of the design, an integral HPF (designed per lecture 2) in front of the mixer will reduce PCS interference at 1800 MHz by at least 20 dB.

• LO_pwr=-10 dBm, Vcc=+5.0 volts, Ic=10 mA max. All transformers are off chip.

Home Work #3: Advanced Wi-Fi Mixer

• Simulate the three isolations, the three matches, P-1dB compressed power, upper and lower OIP3, and the large signal noise figure for the mixer you designed in home work #2.

• Layout your Wi-Fi mixer using Knowledge On design rules. All three radio frequency ports (RF, LO, and IF) are to be pairs of standard bonding pads, spaced by 150 microns (c-c) which can be bonded to three off chip transformers. A 7th pad is Vcc. Keep your layout as “square” as possible.

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