Advanced RFIC Design ELEN359A, Lecture 3: Gilbert Cell Mixers Instructor: Dr. Allen A Sweet
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.
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.
Down Converting Mixer: Applications to Receivers FI=Fl-Fr
Up Converting Mixer: Applications To Transmitters FR=Fl+/-FI LSB USB
Double Balanced Diode Mixer Topology R Virtual Ground L Virtual Ground
Diode IV Characteristics
VBIC Diode IV
ADS Schematic of a Balanced 4 Diode Mixer
HB Controller, Gain Equation and RF Source
LO Source
HB Controller
HB Controller to Sweep RF_pwr
Conversion Loss vs RF_pwr Gain Compression Begins
HB Controller to Sweep LO_pwr
HB Controller to Sweep LO_pwr
Conversion Loss vs LO_pwr (Preamp Requires 20 ma Current to Boost Gain to +10 db) (LO Amp Requires 100 ma Current @ 30 % efficiency)
Single Balance Bipolar Transistor Multiplying Mixer Topology Q1 collector current Controls Transconductance Vi = Vl x Vr
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
Double Balanced (Gilbert Cell) Bipolar Transistor Mixer
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.
A Direct Conversion Receiver using Gilbert Cell Mixers
Gilbert Cell Mixer Topology
Fully Differential Mixer Cell
Series Diode Bias Tree
DC Power and Output Term
RF and LO Sources
HB Controller and Equations
Harmonic Balance Controller
DC Analysis
Bias Tree DC Levels
MIX Function Determines Frequency Index
Basic Simulation Calculates Conversion Gain in Two Ways
LPF Eliminates Spurious Signals in the Mixer s Output
Mixer Simulation including an Output LPF.
HB Controller to Sweep LO_pwr
HB Controller to Sweep LO_pwr
Simulation of Gain vs LO_pwr
HB Controller for Sweeping RF_pwr
HB Controller to Sweep RF_pwr
Simulated Gain vs RF_pwr (P-1dB)
S Parameter Controller Simulates Isolations and Matches
Matches and Isolations of a Gilbert Cell Mixer
Disabling one Transistor Creates Imbalance and Poor Isolation
Gilbert Cell Up Converter (i.e. F2+/-F1)
Up Converting Mixer HB Controller and Equations
Sources for Up Converting Mixer
BPF Selects a USB or an LSB Output
Up Converter Simulation Including MIX Function Table
USB Output is Selected with the BPF
HB Controller and Equations to Simulate OIP3
LO and RF Sources for Intermodulation Simulations
HB Controller-Freq
HB Controller-Sweep
HB Controller- Solver
HB Controller- Params
MIX Function Determines Frequency Index for each Signal
Intermodulation Spectrum
Gain and OIP3(upper and lower) (db) vs LO_pwr (dbm)
LO and RF Sources to Simulate Non Linear Noise Figure
HB Controller and Equations for Noise Figure Simulation
HB Controller-Freq
HB Controller-Params
HB Controller- Noise(1)
HB Controller-Noise (2)
HB Controller-Solver
HB Controller- Output
Simulated ssb Noise Figure
Simulated Noise Figure (dsb) and Conv Gain
Noise Voltage Output at 400 MHz in a 1 Hz Bandwidth
Home Work #2:A Down Converting Mixer for Wi-Fi 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 7 th pad is Vcc. Keep your layout as square as possible.