Anurag Nigam Senior Designer, NatTel Microsystems Pvt. Ltd.

SiGe Low Power Wideband Mixer for 60 GHz RF Front-end for OFDM Applications
Anurag Nigam Senior Designer, NatTel Microsystems Pvt. Ltd. H.P.: , Company site:

NatTel Microsystems Pvt. Ltd.
Design Target Most important design targets are- Data Rate & Bandwidth of the communication system We have chosen WisAir 531 MAC/BB implementation of wireless USB that allows Ethernet USB Bridge and direct streaming of Internet and Video data on to the network. Data Rates up to 480 Mbps are possible. The radio is implemented using 502 RF Chip. For this system a total bandwidth of 1.7 GHz (3.1 GHz to 4.8 GHz) is used. We plan to alter the frequency band to be slightly higher for the ease of design and also better RF-LO Isolation at 60 GHz. Accordingly we will alter the front end of 502 RF Chip and its LO Frequency. We may not require to do this in later revisions if we expect RF-LO Isolation to be sufficient. Choice of RF 60 to 67 GHz band is available as license free band. It is oxygen absorption band. It has few advantages- Due to high absorption by oxygen a smaller micro-cellular layout can be chosen for the network in a cellular broadcast scenario. This allows better spatial frequency reuse and hence higher subscriber capacity. With smaller size antennas high directivity is possible allowing lower path loss and lower interference. In case of cellular broadcast, more sectors in a micro-cell can reuse a frequency. This is efficient spectral usage. NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

Design Centering Choice of IF Input of a Mixer has a hybrid for RF-LO Isolation. Very small IF will result in poor RF-LO isolation. Similarly, very large IF shall result in gain and phase imbalance at the mixer output due to 10 to 15% bandwidth of the coplanar passive components. Passive components at best have bandwidth of 30 to 35% of the center-band frequency. Hence, the lower band edge should at least be 1/0.35 times the target bandwidth i.e. 1/0.35 x 1.7 GHz= 4.8 GHz. Then the higher band edge would be =6.5 GHz. Figure 1: First Down Conversion Frequency (GHz) 57 61.8 63.5 4.8 6.5 LO RF IF Choice of LO Frequency We center the design of the input section to be at 60 GHz. IF band is 4.8 GHz-6.5 GHz. Thus 6.5 GHz is centered around 60 GHz. For this reason, We choose LO frequency to be 57GHz. Choice of LO as 57 GHz establishes the RF band to be 61.8 GHz-63.5 GHz. NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

Principal of Operation
Signal Flow through the Mixer Signal at the output of the Mixer LPF The baseband signal around DC is a common mode input to the subsequent differential stages. Hence, it does not show up at the differential output. Balanced Differential Output Figure 2: Equation Based Modeling of Quadrature Mixer NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

Circuit Topology 1 2 3 4 5 6 7 CMOS Vcc Bipolar Vcc mm-Wave LO IF1 IF2 Figure 3: Circuit Block Diagram based on the functionality of each block NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

Important Sub-Circuits
Mixer 90˚ Hybrid 50 Ω λ/4 Transmission Line 36 Ω λ/4 Transmission Line 60 GHz Bias De-Coupling GHz Bias De-Coupling 56 GHz Reflection Stub 60 GHz Input Match GHz Output Match Bandgap/PTAT/CTAT Bias 1 2 3 4 5 6 7 Various Important Blocks of the Mixer as per design priority are listed in the figure. The design is done in 9 exercises. In Exercise 1, 2, 3, 4, 5, 6, 8, 9 & 10 we design sub-circuits. Exercise 7 is to substitute realistic sub-circuits into the design one by one as we go along Exercises 1 to 10. Exercise 11 is to simulate complete circuit. Exercise 12 is to perform the complete Mixer Layout. Exercise 13 is left as open ended exercise to the participants to craft each sub-circuit as per layout modifications and guarantee the final performance of the Mixer Layout. Figure 4: Mixer Sub-Circuits NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

Circuit Concepts Dual Gate FETs have been used for mixers at high frequencies. Issue with such mixers is RF-to-LO isolation. Leakage of RF into Local Oscillator affects Spectral Purity of the Mixer and degrades its IF output in terms of linearity. Self Demodulation of LO causes DC wandering problem which is difficult to fix. Leakage of LO to RF can reradiate back into space through the antenna. To avoid these effects, a 90˚ Hybrid is used at the input of the Mixer. As proposed in Principle of operation, 90˚ & 180˚ delays are expected at the ports 2 and 3, respectively for mm-Wave while same is expected for LO at the ports 3 and 2, respectively. Isolation is expected between ports 1 & 4. 2 3 4 5 6 7 CMOS Vcc Bipolar Vcc IF1 IF2 1 mm-Wave LO In Exercise 1, 2 and 3 we design 90˚ Hybrid at the input of the mixer operating at 60 GHz. As discussed earlier, 60 GHz is roughly center between LO and RF. 1 2 4 3 Figure 5: 90˚ Hybrid at the input of the Mixer NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

Circuit Concepts Input matching to the bipolar devices should be a broadband matching covering complete frequency band from 57 GHz to 63.5 GHz. Input planes, as shown in the figure, should be matched at mm-Wave band and fully miss-matched at IF band. Series Capacitors that miss-match at IF band and couple at mm-Wave band are difficult to design due to their self resonance. 2 3 4 6 7 CMOS Vcc Bipolar Vcc IF1 IF2 1 mm-Wave LO 5 Matching Planes In Exercise 7 we design a narrow band match at the input using ideal lumped components. In Exercise 8 we layout the input match and EM-Simulate it. Figure 6: Input Match to the bipolar devices NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

Circuit Concepts Output matching to the bipolar devices has to have a bandwidth that is 35% of the center band frequency. It has to be a low pass circuit to reject the higher order mix components. Output Match also has to reflect 57 – 63.5 GHz band by creating a short. Open Circuited Stub marked as 4 in the figure does the same. Output Match, marked 6 in the figure, can be a single pole match and still be broadband due to low parasitics of the bipolar devices. 2 3 7 CMOS Vcc Bipolar Vcc IF1 IF2 1 mm-Wave LO 5 4 6 In Exercise 9 we design low pass match at the output using ideal lumped components. Ideal lumped components are substituted by Output Match Layout and EM Simulated Components. The Open Circuited Stub is design in Exercise 6 Figure 7: Output Match to the bipolar devices NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

Circuit Concepts 57 – 63.5 GHz Bias Decoupling has to be broadband. A large bypass MIM capacitor can not be used due to its self resonance in this bias decoupling. Small capacitor can be designed as bypass capacitor or a radial stub can be used for bypass. 4.8 – 6.5 GHz Bias Decoupling has to be broadband. Instead of using a tank circuit, inductor can be designed to be big enough to anti-resonate at 5.65 GHz. In Exercise 4 we design 57 – 63.5 GHz Bias Decoupling. In Exercise 5 we design 4.8 – 6.5 GHz Bias Decoupling. 5 4 6 7 CMOS Vcc Bipolar Vcc IF1 IF2 1 mm-Wave LO 2 3 62.65 GHz Bias De-Coupling 5.65 GHz Bias De-Coupling Figure 8: GHz and 5.65 GHz Bias De-coupling Circuits NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

Circuit Concepts Bias Circuit has two distinct sections- PTAT Current Source and CTAT Voltage Source. Brokaw Cell is used as Bandgap Voltage Reference. The output section of the bias circuit has an Op-Amp Buffer and a Voltage to Current Converter. In Exercise 10 we design PTAT Current Source, CTAT Voltage Source, Brokaw Bandgap Reference and Voltage to Current Converter. Depending on the across-temperature performance of the mixer, we can tweak appropriate resistors to provide PTAT, CTAT or Bandgap performance. 2 3 4 6 CMOS Vcc Bipolar Vcc IF1 IF2 1 mm-Wave LO 5 7 Figure 9: On-Chip Temperature Compensated Bias Circuit NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

Metal Stack for IHP SG25 TM1TM2
TopMetal2 TopVia2 TopMetal1 TopVia1 Metal3 Via2 Metal2 Via1 Metal1 MIM Figure 10: Metal Stack for IHP Process NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

Ideal Hybrid Design Use ideal transmission line components in ADS to design a Hybrid as shown in figure. λ/4 Electrical Length 1 2 3 4 Establishing Impedances Establishing Power Consider for analysis that power is put in port 1 and 4 as Even and Odd Modes with amplitudes +-1/2. Figures 16 and 17 show circuit for Even and Odd Modes. The superimposition will show that power is put only in port 1 while port 4 is matched to characteristic impedance. For simplicity all impedances and terminations are normalized. Figure 11: Ideal 90˚Hybrid Design λ/4 λ/8 1 Figure 12: Even Mode Impedances +1/2 Figure 13: Odd Mode Impedances λ/4 λ/8 1 +1/2 -1/2 NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

90˚ Hybrid Design & Layout
Design 36 Ω and 50 Ω Quarter wave lines. Connect them as shown in the figure. Bring out ports using 50 Ω lines. Save the file as “Hybrid60GHz.dsn”. Port 1 Port 4 Port 2 Port 3 Figure 14: 3D View of the designed 90˚ Hybrid Attach and properly define the ports. Perform EM Simulations at 60 GHz. Adjust the dimensions of each branch for optimum performance. Figure 15: Layout of the designed 90˚ Hybrid NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

Simulating 90˚Hybrid across frequency
Setup S-Parameter Simulation Schematic as shown in the figure. Save the file as “TestHybrid.dsn”. Figure 16: EM Simulation Response of 90˚ Hybrid across frequency This concludes the design of the Hybrid as Input Section of the Mixer NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

Role of 60 GHz Bias De-Coupling
Bias Decoupling is used to isolate RF Circuit from the DC Supply current source. For DC, the decoupling looks like a short providing proper DC base current to the active devices while for RF it looks like an open. This allows tuning at the input at the desired frequency. A short has to be generated for RF on the supply side so that irrespective of the output impedance of the current source, the match at the input does not degrade. Bias Decoupling can take one of the three forms shown below. Option A Option B Option C RF DC λ/4 RF DC λ/4 RF DC Figure 17: Bias Decoupling using lumped components Figure 18: Bias Decoupling using stubs Figure 19: Bias Decoupling using mixed components Option A is not possible at high frequencies due to self resonance of passive components. Option B is best suited for high frequency but occupies large chip area. Option C is slightly degraded in performance but occupies smaller area. We will explore Option B and Option C for our design. NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

Option C- Bias Decoupling @ 57-64 GHz
Design 0.6pf or smaller (MIM) Capacitor and 50 Ω Quarter-Wavelength long line. Connect them as in the figure. Perform EM Simulations. Alter length for performance. Refer to the instructor for further details. Save the file as “BiasDeCoup60GHz.dsn”. Adjust the cap size and length to maximize decoupling and save the layout as “DeCoup60GHz.dsn”. Re-simulate the circuit to see the improvement. Figure 20: Bias Decoupling Layout at GHz Port 2 Figure 21: Bias Decoupling at GHz Port 1 NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

Option C- Bias Decoupling Response
Plot S11 and S22 for 60 GHz decoupling layout in “DeCoup60GHz.dsn. Place the markers at the fundamental frequencies i.e. 57 GHz, 61.8 GHz & 63.5 GHz Figure 22: Response of Bias Decoupling (Optimized) at GHz This concludes the design of Bias Decoupling at GHz NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

Option A- 4.8 – 6.5 GHz Bias Decoupling
Design a 4.6 pf Capacitor and an inductor large enough to anti-resonate in the desired frequency band of 4.8 – 6.5 GHz. Connect them as shown in the figure. Add ports and edit them appropriately. Perform EM Simulations. Save the file as “BiasDeCoup5_65GHz.dsn” Figure 23: Layout of Bias Decoupling at 4.8 – 6.5 GHz Port 2 Figure 24: Bias Decoupling at 4.8 – 6.5 GHz Port 1 NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

EM Simulation Response of 4.8 – 6.5 GHz Bias Decoupling
Plot S11, S22 & S21. Place markers at 4.8 GHz & 6.5 GHz Figure 25: EM Simulation Response of Bias Decoupling at 4.8 – 6.5 GHz This concludes the design of Bias Decoupling at GHz NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

57 GHz Open Circuited Stub Design
Design a 50 Ω Quarter Wavelength long CPWG 57 GHz. Attach the ports and edit them appropriately. Perform EM Simulations. Figure 26: Layout of the Open Circuited Stub at the output of the Mixer Figure 27: Open Circuited Stub at the output of the Mixer NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

Simulation of 57 GHz Open Circuited Stub
Setup S-Parameter Simulation as shown in the figure and perform simulation. Add marker to S11 57 GHz Figure 28: Response of Open Circuited Stub used to generate short at the 57 GHz This concludes the design of Open Circuited Stub at 56.5 GHz NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

Tuned Active Circuit Response
Choose a small HBT device with low parasitics. Bias it appropriately. Use EM Simulated Bias Decoupling at input and output and open circuited stub at the output. Figure 29: Response of Active circuit of the mixer, biased through bias decoupling, matched at input to GHz and at output to GHz NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

Active Circuit in Mixer Schematic
Connect two tuned Active Circuits and Hybrid as shown in the figure Figure 30: Mixer Circuit Schematic NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

Complete Bandgap Current Source
Design the Brokaw Cell, Op-Amp and Output Voltage to Current Converter and connect them as shown in the figure. Figure 31: Complete Bandgap Referenced Current Source NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

Bias Circuit Layout Layout the bias circuit as shown in the figure Figure 32: Complete Bandgap Referenced Current Source Layout NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

HB Simulation of the Mixer
Connect the bias circuit and the mixer component. Setup Harmonic Balance Simulations to simulate the down conversion response of the mixer across the RF Frequency. Figure 33: Across frequency Harmonic Balance Simulation of Mixer NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

Across RF Frequency of the Mixer
Set the RF Power to -5 dBm and LO Power to 0 dBm. Sweep the frequency across the band of interest and plot the results Figure 34: Across frequency Response of the Mixer NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

Compression Characteristics of the Mixer
Set the RF to GHz and LO Power to 0 dBm. Sweep the RF Power and plot the results Figure 35: Across Power Response of the Mixer NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

Mixer Layout Figure shows layout of the Mixer in IHP SiGe Bi-CMOS Process GSGSG RF LO IF+ IF- VDC1 VDC2 Figure 36: 3D EM Preview of the Mixer NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

Concluding Remarks We can conclude the following about the Mixer Design Die Size 900 um x 700 um Two DC Supplies- 1.8 V and 3.3 V Quiescent Current of 6 mA from 1.8 V supply and 1.7 mA from 3.3 V supply Across band conversion loss better than 1 dB -1 dB Input Compression at -3.6 dBm RF input LO is 57 GHz and 0 dBm RF is 61.8 to 63.5 GHz IF is 4.8 to 6.5 GHz Noise Figure better than 12 dB Temperature Compensated Bias Circuit (-40 to 85 Degree Celsius ) Phase Balance better than 3 degrees Gain Balance better than 0.5 dB NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

SiGe Low Noise Amplifier for 60 GHz RF Front-end for OFDM Applications
Anurag Nigam Senior Designer, NatTel Microsystems Pvt. Ltd. H.P.: , Company site:

Design Target Most important design target is- Low Noise Figure (Noise Factor) of the Low Noise Amplifier Passive Mixers are the best in terms of noise figure but do not offer sufficient conversion gain. Active mixers provide best conversion gain but are noisy. Both are desirable electrical characteristics. In former case an amplifier at the input would improve the gain of the two stages thus improving sensitivity of the receiver. In latter case an amplifier at the input will reduce the noise of the mixer referred to antenna thus improving the sensitivity of the receiver. Receiver Sensitivity Figure 1: LNA-Mixer at input of the receiver Receiver Sensitivity (V) Noise Factor at the receiver input Boltzmann’s Constant (J/K) Receiver Bandwidth (Hz) Ambient Temperature (K) Minimum S/N Ratio at the detector Characteristic Impedance (Ω) Mixer LNA IF+ IF- Local Oscillator (57 GHz) (4.8 – 6.5 GHz) (61.8 – 63.5 GHz) Noise Factors Minimum Signal strength that can be detected by the receiver faithfully is called “Receiver Sensitivity” Gain NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

Diminishing Returns Noise Figure Data from IHP Process Manual Measured Data Simulated Data (Loss De-embedded) Figure 2: npn 200_8 device NFmin (dB) Vs Frequency. Note that at 60 GHz (either using extrapolation or ADS Simulation) the NFmin = 4.5 dB Figure 3: npn 200_8 device NFmin (dB) Vs Base Bias. For gain and stability each stage has to be biased slightly above the required base voltage of 0.84 V for NFmin. This results in 1.2 times the NFmin at 0.88V base bias. At 60 GHz (either using extrapolation or ADS Simulation) at 0.88V biasing the NFmin = 5.4 dB For a tuned common emitter stage, the 60 GHz is 4.7dB. NFmin is 5.2 dB and the losses in matches are 1.4 dB. Over all Noise Figure of the tuned stage with losses is expected to be slightly above 6 dB. Clearly the process has very poor performance at 60 GHz for LNA Design. NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

Lets give it a try! The process is not bad for learning the design flow for LNA Design. So we will go forward with the design so as to demonstrate the design flow. Bias Circuit Match 1 Match 2 Match 3 Match 4 Match 5 Bias De-Coupling 1 Bias De-Coupling 2 By-Pass LNA 60 GHz Bias De-Coupling 1 2 3 4 5 Cascode Gain Stage Common Emitter Gain Stage Common Base Gain Stage Two Stage Cascode LNA Figure 4: LNA Sub-Circuits Figure 5: Two Stage Cascode LNA NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

LNA Design Using the design techniques developed during mixer design, a Cascode Gain Stage is Designed as shown in the ADS Schematic. Figure 6: Design & S-Parameter Simulation of Cascode LNA NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

Small Signal Response of the LNA
Figure shows final S-Parameter Response of the designed LNA. Bandgap Bias Circuit designed for the mixer is reused. Figure 7: S-Parameter Response of Cascode LNA NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

LNA Layout GSG Output GSG Input VDC Figure 8: 3D EM Preview of the LNA NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

LNA Schematic with Bias Circuit
Figure 9: Brokaw Cell based Bandgap Reference Bias Circuit is included in the simulations NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

LNA Layout with Bias Circuit
Figure 10: Single Stage Cascode LNA Layout with Bandgap Reference Bias Circuit NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

Concluding Remarks We can conclude the following about the LNA Design Die Size 440 um x 430 um DC Supplies V Quiescent Current of 17 mA Gain > 7.6 dB Return Losses < -10 dB Noise Figure 7.2 dB Temperature Compensated Bias Circuit (-40 to 85 Degree Celsius ) NatTel Microsystems Pvt. Ltd. Engraving the beginning of a New Era in Technologies

Anurag Nigam Senior Designer, NatTel Microsystems Pvt. Ltd.

Similar presentations

Presentation on theme: "Anurag Nigam Senior Designer, NatTel Microsystems Pvt. Ltd. "— Presentation transcript:

Similar presentations

About project

Feedback

Log in

Auth with social network:

Anurag Nigam Senior Designer, NatTel Microsystems Pvt. Ltd.

Similar presentations

Presentation on theme: "Anurag Nigam Senior Designer, NatTel Microsystems Pvt. Ltd. "— Presentation transcript:

Similar presentations

About project

Feedback