Advanced RFIC Design ELEN359A, Lecture 3: Gilbert Cell Mixers. Instructor: Dr. Allen A Sweet

Transcription

1 Advanced RFIC Design ELEN359A, Lecture 3: Gilbert Cell Mixers Instructor: Dr. Allen A Sweet

2 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.

3 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.

4 Down Converting Mixer: Applications to Receivers FI=Fl-Fr

5 Up Converting Mixer: Applications To Transmitters FR=Fl+/-FI LSB USB

6 Double Balanced Diode Mixer Topology R Virtual Ground L Virtual Ground

7 Diode IV Characteristics

8 VBIC Diode IV

9 ADS Schematic of a Balanced 4 Diode Mixer

10 HB Controller, Gain Equation and RF Source

11 LO Source

12 HB Controller

13 HB Controller to Sweep RF_pwr

14 Conversion Loss vs RF_pwr Gain Compression Begins

15 HB Controller to Sweep LO_pwr

16 HB Controller to Sweep LO_pwr

17 Conversion Loss vs LO_pwr (Preamp Requires 20 ma Current to Boost Gain to +10 db) (LO Amp Requires 100 ma 30 % efficiency)

18 Single Balance Bipolar Transistor Multiplying Mixer Topology Q1 collector current Controls Transconductance Vi = Vl x Vr

19 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

20 Double Balanced (Gilbert Cell) Bipolar Transistor Mixer

21 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.

22 A Direct Conversion Receiver using Gilbert Cell Mixers

23 Gilbert Cell Mixer Topology

24 Fully Differential Mixer Cell

25 Series Diode Bias Tree

26 DC Power and Output Term

27 RF and LO Sources

28 HB Controller and Equations

29 Harmonic Balance Controller

30 DC Analysis

31 Bias Tree DC Levels

32 MIX Function Determines Frequency Index

33 Basic Simulation Calculates Conversion Gain in Two Ways

34 LPF Eliminates Spurious Signals in the Mixer s Output

35 Mixer Simulation including an Output LPF.

36 HB Controller to Sweep LO_pwr

37 HB Controller to Sweep LO_pwr

38 Simulation of Gain vs LO_pwr

39 HB Controller for Sweeping RF_pwr

40 HB Controller to Sweep RF_pwr

41 Simulated Gain vs RF_pwr (P-1dB)

42 S Parameter Controller Simulates Isolations and Matches

43 Matches and Isolations of a Gilbert Cell Mixer

44 Disabling one Transistor Creates Imbalance and Poor Isolation

45 Gilbert Cell Up Converter (i.e. F2+/-F1)

46 Up Converting Mixer HB Controller and Equations

47 Sources for Up Converting Mixer

48 BPF Selects a USB or an LSB Output

49 Up Converter Simulation Including MIX Function Table

50 USB Output is Selected with the BPF

51 HB Controller and Equations to Simulate OIP3

52 LO and RF Sources for Intermodulation Simulations

53 HB Controller-Freq

54 HB Controller-Sweep

55 HB Controller- Solver

56 HB Controller- Params

57 MIX Function Determines Frequency Index for each Signal

58 Intermodulation Spectrum

59 Gain and OIP3(upper and lower) (db) vs LO_pwr (dbm)

60 LO and RF Sources to Simulate Non Linear Noise Figure

61 HB Controller and Equations for Noise Figure Simulation

62 HB Controller-Freq

63 HB Controller-Params

64 HB Controller- Noise(1)

65 HB Controller-Noise (2)

66 HB Controller-Solver

67 HB Controller- Output

68 Simulated ssb Noise Figure

69 Simulated Noise Figure (dsb) and Conv Gain

70 Noise Voltage Output at 400 MHz in a 1 Hz Bandwidth

71 Home Work #2:A Down Converting Mixer for Wi-Fi Design a Down Converting Gilbert Cell Mixer for B (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.

72 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.