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(1) This document describes a Class-G headphone amplifier designed by Alex Lollio for his Ph.D. research. It compares different amplifier classes and proposes a Class-G solution. (2) A prototype was implemented in 65nm CMOS technology. Measurement results showed 50% lower power consumption than competing designs while achieving over 80dB THD and 101dB SNR. (3) An improved 4-stage version was then proposed to meet a new 110dB SNR specification. Simulation results indicated it could achieve the same performance as the original design but using only 1/3 of the capacitor area and 10% more power.

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Class-G Headphones Amplifier Universit di Pavia - Dipartimento di Elettronica Dottorato di Ricerca in Microelettronica - XXIII Ciclo Ph.D. Candidate: Alex Lollio TUTORE: CHIAR.MO PROF. RINALDO CASTELLO COORDINATORE: CHIAR.MO PROF. FRANCO MALOBERTI
Headphone audio amplifiers Target application Typical operating conditions VIN VHV -VHV Key objectives: ≒Low distortion ≒Low noise ≒High efficiency ≒Single ended ≒RL = 32/16 立 ≒BW = 20Hz20kHz ≒PO,MAX > 40mW (on 16 立) Modern cellular phones incorporates music playback and users may wish to use this feature for many hours 1/28
Outline ≒ Headphone amplifier (Class-AB, Class-D, Class-G PROs and CONs) ≒ Class-G headphone driver (architecture, switching principle, distortion analysis) ≒ Prototype in 65nm CMOS technology (implementation, results, comparison) ≒ Class G improved version (new SNR Spec, proposed solution, results and comparison) ≒ Conclusions
Outline ≒ Headphone amplifier (Class-AB, Class-D, Class-G PROs and CONs) ≒ Class-G headphone driver (architecture, switching principle, distortion analysis) ≒ Prototype in 65nm CMOS technology (implementation, results, comparison) ≒ Class G improved version (new SNR Spec, proposed solution, results and comparison) ≒ Conclusions
Class AB (Linear amplifier) PROs: Best linearity No EMI problems CONs: Low efficiency Typically the preferred solution in headphone application Class D (Switching amplifier) PROs: Best efficiency CONs: Less linearity than class AB EMI problems Emerging solution in headphone application Headphone audio amplifiers Alternative topologies 2/28
Class G: It is a linear amplifier which uses two voltage supply rails which switches to the appropriate voltage as required by the instantaneous output voltage PROs: High efficiency but less than class D High linearity but less than class AB No EMI problems CONs: It needs two voltage supply rails Headphone audio amplifiers Alternative topologies VIN VLV VHV -VLV -VHV VHV -VHV VLV -VLV VOUT VOUT 3/28
Class G alternative topologies Series topology (classical) Parallel topology ≒Only one output stage ≒Switches are in series with the power transistors ≒Two output stages work in parallel ≒No switches in series with the power transistors ≒It needs a careful switching circuit design VHV -VHV VLV -VLV VHV VLV -VHV -VLV RL RL This is the adopted solution 4/28
Class G: working principle For Vout below the switching point the low voltage stage is active. For Vout above the switching point both the low voltage and high voltage stages drive the load (in different moments). VHV VLV -VHV -VLV LV stage HV stage iHV iLV iLV iHV iLV iHV Iout[A] Iout[A] iLV t t Switching point 5/28
9 Class G: switching distortion Distortion zoom in Distortion caused by the switching Up to the switching point the class G linearity is the same as a class AB Compared to class AB, class G has an additional source of distortion. Switching point 6/28
The implemented current based switching enables low distortion and high efficiency Class G: critical design choices ≒Switching point level: To achieve high efficiency, it must be as close as possible to the low voltage supply Switching point equal to VLV (efficiency=78%) Switching point far from the low voltage supply ≒Switching strategy: to minimize the distortion, switching must be as smooth as possible 7/28
Outline ≒ Headphone amplifier (Class-AB, Class-D, Class-G PROs and CONs) ≒ Class-G headphone driver (architecture, switching principle, distortion analysis) ≒ Prototype in 65nm CMOS technology (implementation, results, comparison) ≒ Class G improved version (new SNR Spec, proposed solution, results and comparison) ≒ Conclusions
Overall amplifier architecture ≒Three stage opamp with differential input and single ended output. ≒The two identical second stages, gm2, and the third stages, gm3L and gm3H, work in parallel. ≒Only the low voltage stage gm3L is supplied by the low voltage rail 賊VLV. The rest of the circuit is supplied by the high voltage rail 賊VHV gm2 gm2 gm1 -gm3L -gm3H Switching stage R2 R1 R1 R2 RL CM2 CM2CM1 VOUT Main path 8/28
13 Amplifier architecture: main path First stage Input pairs gm1 VO VLV -VLV VHV -VHV Floating battery VHV VHV -VHV RL 9/28
14 Second stage Amplifier architecture: main path gm2 Floating battery ref: Renirie, Langen, Huijsing, 1995 VO VLV -VLV VHV -VHV Floating battery VHV VHV -VHV RL 10/28
15 Amplifier architecture: main path Third stage LV stage gm3L HV stage gm3H RL VO VLV -VLV VHV -VHV -VHV Floating battery VHV VHV 11/28
-VLV + VTH Amplifier architecture: switching stage conceptual schematic PMOS switching stage NMOS switching stage RL VO VO VLV - VTH VO VLV -VLV VHV -VHV -VHV Floating battery VHV VHV 12/28
-VLV + VTH Amplifier architecture: switching stage conceptual schematic PMOS switching stage RL VO VO VLV - VTH VO VLV -VLV VHV -VHV -VHV Floating battery VHV VHV 13/28
≒Switching point sensing is in voltage domain. A differential pair compares the output voltage to the switching point voltage VLV-VTH ≒The switching between the high voltage and low voltage output stage is current based. The switching circuit injects all its bias current into the gate of the MOS to be switched off. Switching principle details VOUT LV stage HV stage iJH iJL VOUT VLV - VTH VHV -VHV -VLV VLV VHV VHV IBIAS PMOS switching stage 14/28
Output currents during switching t Iout[A] Outputcurrents iLV iHV t VLV -VTH VLV Vout[V] ≒When VOUT is lower than the switching point (VLV-VTH) the switching circuit enables the LV stage and disables the HV stage ≒When VOUT is higher than the low voltage supply VLV only the HV stage drives the load ≒When VOUT is between VLV-VTH and VLV both stages drive the load 15/28
Switching distortion: Amplifier model during the switching ≒We use a simplified linear model of the amplifier during the switching. This current is used to represent the disturbance generated by the switching stage. gm1 gm2 -gm3 RL VOUT R1 R1 R2 CM1 CM2 iJ Where R2 16/28
Outline ≒ Headphone amplifier (Class-AB, Class-D, Class-G PROs and CONs) ≒ Class-G headphone driver (architecture, switching principle, distortion analysis) ≒ Prototype in 65nm CMOS technology (implementation, results, comparison) ≒ Class G improved version (new SNR Spec, proposed solution, results and comparison) ≒ Conclusions
Chip micrograph ≒ 65nm CMOS process (1.8V analog transistors) ≒ 0.14mm2 active area per channel ≒ Voltage supplies: High voltage rail 賊1.4V Low voltage rail 賊0.35V ≒ Switching point 50mV under the low voltage supply ≒ Max load capacitance 1nF 17/28
23 Measurement results: Power dissipation versus output power Fin=1kHz RL=32立 18/28
Measurement results: THD+N and efficiency versus output power ≒Sinusoidal input signal (fin=1kHz) ≒About 6dB extra distortion due to switching 19/28
Performance summary and comparison with literature Parameter This work (Class G) JSSC 09 (Class AB) [1] ESSCIRC 06 (Class AB) [2] ISCAS 09 (Class D) [3] Technology 65nm 130nm 65nm 0.13um Supply voltage 賊1.4V 賊0.35V 賊1V 賊0.6V 2.5V 3.6V Quiescent power (per channel) 0.41mW 1.2mW 12.5mW 1.8mW Peak load power (16立) 90mW 40mW 53.5mW 50mW THD+N @ PRMS (32立) -80dB @ 16mW -84dB @ 10mW -68dB @ 27mW (16立) -80dB @ 10mW SNR A-weighted 101dB 92dB (un- weighted) - 96dB [1] Vijay Dhanasekaran, JSCC 09 [2] P. Bogner, ESSCIRC 06 [3] Pillonet, ISCAS 09 20/28
Performance comparison with products Parameter This work (Class G) MAX9725 (Class AB) TPA6141 (Class G) LM48824 (Class G) Supply voltage 1.4V with two charge pumps + 1 buck 1.5V with one charge pump 3.6V with 1 charge pump + 1 buck 3.6V with 1 charge pump + 1 buck Quiescent power (per channel) 0.41mW + 0.3mW (2 CPs + 1 buck) 1.57mW 2.16mW 1.62mW PSUP @ PL=0.1mW 0.87mW + 0.4mW - 4.5mW 3.24mW PSUP @ PL=0.5mW 1.63mW + 0.6mW - 7.2mW 5.58mW Peak load power (16立) 90mW 70mW (CPs RON=2.5立) 50mW 50mW 74mW THD+N @ PRMS (32立) -80dB @ 16mW -84dB @12mW -80dB @20mW -69dB@20mW SNR A-weighted 101dB 92dB 105dB 102dB 21/28
Outline ≒ Headphone amplifier (Class-AB, Class-D, Class-G PROs and CONs) ≒ Class-G headphone driver (architecture, switching principle, distortion analysis) ≒ Prototype in 65nm CMOS technology (implementation, results, comparison) ≒ Class G improved version (new SNR Spec, proposed solution, results and comparison) ≒ Conclusions
New Spec: increase the SNR of 10dB 3-stages improved performance Aim: increase the SNR Classical approach: increase gM1 and consequently CM1 ISCC 10 3-stages improved SNR @ 1VRMS 100dB 110dB CM1 15pF 260pF CM2 4x18pF 4x18pF PQ 0.41mW 0.55mW Big area where 22/28
4-stages Feed Forward (FF) solution ≒ The additional stages increase the open loop gain of the amplifier at low frequencies ≒ The stage gM11 dominates the noise performance Additional stages Ref: A. Bosi et all. VDSL2 Analog Front End, ISSCC, 2009 23/28
4-stages Feed Forward (FF) solution ≒ The amplifier cuf off frequency is gM1/CM1 ≒ The GLOOP shows a zero at Low freq path High freq path High freq path gM1 Low freq path gM11/sC 揃 gM12 24/28
4-stages FF: GLOOP plot 4-stages FF solution: 1. gM11 determines the noise performances 2. More open-loop gain in the audio BW Audio BW (20Hz-20kHz) 25/28
4-stages FF: Less capacitors sizes 3-stages improved performance: 4-stages FF: gM11 determines the noise performance Big area Audio BW (20Hz-20kHz) 26/28
4-stages FF: Less switching distortion 4-stages FF shows higher switching distortion compression We can reduce gM2 saving power consumption We can reduce CM2 saving area 3-stages: 4-stages FF: 3-stages 4-stages FF gM2 200uA/V 55uA/V CM2 4x18pF 4x5pF THD@1kHz -82dB -85dB We saved additional 52pF Switching distortion Switching distortion 27/28
Performance summary ISCC 10 3-stages improved 4-stages FF SNR@1VRMS 100dB 110dB 110dB CTOT 87pF 332pF 101pF PQ 0.41mW 0.55mW 0.6mW THD@1kHz -82dB -82dB -85dB Conclusion: The adopted solution shows the same performance as the 3-stages one using 1/3 of total capacitors area paying only 10% of additional power consumption. 28/28
Outline ≒ Headphone amplifier (Class-AB, Class-D, Class-G PROs and CONs) ≒ Class-G headphone driver (architecture, switching principle, distortion analysis) ≒ Prototype in 65nm CMOS technology (implementation, results, comparison) ≒ Conclusions
Conclusions ≒ A class-G headphone driver has been presented. It shows 50% less power consumption than the best competitor. ≒ The class-G improved version satisfies the most aggressive market requirements (110dB of SNR and better than 80dB of THD) ≒ The class-G improved version will be integrated in Dec 2010 into a novel Marvell audio codec
Publications ≒ Marvell Patent Ref No. MP3391: A. Lollio, G. Bollati, R. Castello, CIRCUITS AND METHODS FOR AMPLIFYING SIGNALS ≒ A. Lollio, G. Bollati, R. Castello, Class-G Headphone Driver in 65nm CMOS Technology, Proc. ISSCC 2010, San Francisco, 7-11 Feb. 2010, pp.84-85 ≒ A. Lollio, G. Bollati, R. Castello, A Class-G Headphone Amplifier in 65nm CMOS Technology IEEE J. Solid-State Circuits, vol. 45, no. 12, Dec. 2010.
Activities Summary Seminari organizzati dal dottorato (3.8 CFU) Scuole di Dottorato (12 CFU) Corso Elementi di Elettronica di Potenza (5 CFU) Corso di Misure Elettriche (5 CFU) Tutorato di Elettronica (2 CFU) Presentazione a Congresso Internazionale: ISSCC2010 (3 CFU) Pubblicazione su rivista internazionale: JSSC2010 (4 CFU) Presentazioni annuale sullattivit di ricerca svolta (1.5 CFU) Totale CFU: 36.3
Buck and CPs: Power consumption estimation (per channel) 2 Charge pumps PQ -> 0.2mW 1 Buck (80% efficiency), PL=0 Pdiss -> 0.1mW 1 Buck (80% efficiency), PL=0.1mW Pdiss -> 0.2mW 1 Buck (80% efficiency), PL=0.5mW Pdiss -> 0.4mW Total power consumption PQ -> 0.2mW+0.1mW = 0.3mW PL=0.1mW -> 0.2mW+0.2mW = 0.4mW PL=0.5mW -> 0.2mW+0.4mW = 0.6mW
Measurement results: THD+N versus frequency RL=32立 BW= 20Hz 20 kHz
41 Measurement results: Spectrum at different output power PO=20mW Fin=1kHz PO=1mW Fin=1kHz
[1] Vijay Dhanasekaran; Jose Silva-Martinez; Edgar Sanchez-Sinencio, "Design of Three-Stage Class-AB 16Ohm Headphone Driver Capable of Handling Wide Range of Load Capacitance," Solid-State Circuits, IEEE Journal of , vol.44, no.6, pp.1734-1744, Jun 2009. [2] P. Bogner, H. Habibovic and T. Hartig, A High Signal Swing Class AB Earpiece Amplifier in 65nm CMOS Technology, Proc. ESSCIRC, pp.372-375, 2006. [3] Pillonet, G., et al,A 0.01% THD, 70dB PSRR Single Ended Class D using variable hysteresis control for Headphone Amplifiers, ISCAS 2009 pp.1181-1184. [4] Maxim, 1V, Low-Power, DirectDrive, Stereo Headphone Amplifier with Shutdown, Rev. 3; 8/08, accessed on Jul. 7, 2009 < http://datasheets.maximic. com/en/ds/MAX9725.pdf> [5] Texas Instrument, Class-G Directpath Stereo Headphone Amplifier, 3/09, accessed on Jul. 7, 2009 < http://focus.ti.com/lit/ds/symlink/tpa6141a2.pdf> [6] National Semiconductor Class G Headphone Amplifier with I2C Volume Control, August 31,2009, accessed on Jan. 25, 2010 < http://www.national.com/ds/LM/LM48824.pdf > References

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Lollio10 r

  • 1. Class-G Headphones Amplifier Universit di Pavia - Dipartimento di Elettronica Dottorato di Ricerca in Microelettronica - XXIII Ciclo Ph.D. Candidate: Alex Lollio TUTORE: CHIAR.MO PROF. RINALDO CASTELLO COORDINATORE: CHIAR.MO PROF. FRANCO MALOBERTI
  • 2. Headphone audio amplifiers Target application Typical operating conditions VIN VHV -VHV Key objectives: ≒Low distortion ≒Low noise ≒High efficiency ≒Single ended ≒RL = 32/16 立 ≒BW = 20Hz20kHz ≒PO,MAX > 40mW (on 16 立) Modern cellular phones incorporates music playback and users may wish to use this feature for many hours 1/28
  • 3. Outline ≒ Headphone amplifier (Class-AB, Class-D, Class-G PROs and CONs) ≒ Class-G headphone driver (architecture, switching principle, distortion analysis) ≒ Prototype in 65nm CMOS technology (implementation, results, comparison) ≒ Class G improved version (new SNR Spec, proposed solution, results and comparison) ≒ Conclusions
  • 4. Outline ≒ Headphone amplifier (Class-AB, Class-D, Class-G PROs and CONs) ≒ Class-G headphone driver (architecture, switching principle, distortion analysis) ≒ Prototype in 65nm CMOS technology (implementation, results, comparison) ≒ Class G improved version (new SNR Spec, proposed solution, results and comparison) ≒ Conclusions
  • 5. Class AB (Linear amplifier) PROs: Best linearity No EMI problems CONs: Low efficiency Typically the preferred solution in headphone application Class D (Switching amplifier) PROs: Best efficiency CONs: Less linearity than class AB EMI problems Emerging solution in headphone application Headphone audio amplifiers Alternative topologies 2/28
  • 6. Class G: It is a linear amplifier which uses two voltage supply rails which switches to the appropriate voltage as required by the instantaneous output voltage PROs: High efficiency but less than class D High linearity but less than class AB No EMI problems CONs: It needs two voltage supply rails Headphone audio amplifiers Alternative topologies VIN VLV VHV -VLV -VHV VHV -VHV VLV -VLV VOUT VOUT 3/28
  • 7. Class G alternative topologies Series topology (classical) Parallel topology ≒Only one output stage ≒Switches are in series with the power transistors ≒Two output stages work in parallel ≒No switches in series with the power transistors ≒It needs a careful switching circuit design VHV -VHV VLV -VLV VHV VLV -VHV -VLV RL RL This is the adopted solution 4/28
  • 8. Class G: working principle For Vout below the switching point the low voltage stage is active. For Vout above the switching point both the low voltage and high voltage stages drive the load (in different moments). VHV VLV -VHV -VLV LV stage HV stage iHV iLV iLV iHV iLV iHV Iout[A] Iout[A] iLV t t Switching point 5/28
  • 9. 9 Class G: switching distortion Distortion zoom in Distortion caused by the switching Up to the switching point the class G linearity is the same as a class AB Compared to class AB, class G has an additional source of distortion. Switching point 6/28
  • 10. The implemented current based switching enables low distortion and high efficiency Class G: critical design choices ≒Switching point level: To achieve high efficiency, it must be as close as possible to the low voltage supply Switching point equal to VLV (efficiency=78%) Switching point far from the low voltage supply ≒Switching strategy: to minimize the distortion, switching must be as smooth as possible 7/28
  • 11. Outline ≒ Headphone amplifier (Class-AB, Class-D, Class-G PROs and CONs) ≒ Class-G headphone driver (architecture, switching principle, distortion analysis) ≒ Prototype in 65nm CMOS technology (implementation, results, comparison) ≒ Class G improved version (new SNR Spec, proposed solution, results and comparison) ≒ Conclusions
  • 12. Overall amplifier architecture ≒Three stage opamp with differential input and single ended output. ≒The two identical second stages, gm2, and the third stages, gm3L and gm3H, work in parallel. ≒Only the low voltage stage gm3L is supplied by the low voltage rail 賊VLV. The rest of the circuit is supplied by the high voltage rail 賊VHV gm2 gm2 gm1 -gm3L -gm3H Switching stage R2 R1 R1 R2 RL CM2 CM2CM1 VOUT Main path 8/28
  • 13. 13 Amplifier architecture: main path First stage Input pairs gm1 VO VLV -VLV VHV -VHV Floating battery VHV VHV -VHV RL 9/28
  • 14. 14 Second stage Amplifier architecture: main path gm2 Floating battery ref: Renirie, Langen, Huijsing, 1995 VO VLV -VLV VHV -VHV Floating battery VHV VHV -VHV RL 10/28
  • 15. 15 Amplifier architecture: main path Third stage LV stage gm3L HV stage gm3H RL VO VLV -VLV VHV -VHV -VHV Floating battery VHV VHV 11/28
  • 16. -VLV + VTH Amplifier architecture: switching stage conceptual schematic PMOS switching stage NMOS switching stage RL VO VO VLV - VTH VO VLV -VLV VHV -VHV -VHV Floating battery VHV VHV 12/28
  • 17. -VLV + VTH Amplifier architecture: switching stage conceptual schematic PMOS switching stage RL VO VO VLV - VTH VO VLV -VLV VHV -VHV -VHV Floating battery VHV VHV 13/28
  • 18. ≒Switching point sensing is in voltage domain. A differential pair compares the output voltage to the switching point voltage VLV-VTH ≒The switching between the high voltage and low voltage output stage is current based. The switching circuit injects all its bias current into the gate of the MOS to be switched off. Switching principle details VOUT LV stage HV stage iJH iJL VOUT VLV - VTH VHV -VHV -VLV VLV VHV VHV IBIAS PMOS switching stage 14/28
  • 19. Output currents during switching t Iout[A] Outputcurrents iLV iHV t VLV -VTH VLV Vout[V] ≒When VOUT is lower than the switching point (VLV-VTH) the switching circuit enables the LV stage and disables the HV stage ≒When VOUT is higher than the low voltage supply VLV only the HV stage drives the load ≒When VOUT is between VLV-VTH and VLV both stages drive the load 15/28
  • 20. Switching distortion: Amplifier model during the switching ≒We use a simplified linear model of the amplifier during the switching. This current is used to represent the disturbance generated by the switching stage. gm1 gm2 -gm3 RL VOUT R1 R1 R2 CM1 CM2 iJ Where R2 16/28
  • 21. Outline ≒ Headphone amplifier (Class-AB, Class-D, Class-G PROs and CONs) ≒ Class-G headphone driver (architecture, switching principle, distortion analysis) ≒ Prototype in 65nm CMOS technology (implementation, results, comparison) ≒ Class G improved version (new SNR Spec, proposed solution, results and comparison) ≒ Conclusions
  • 22. Chip micrograph ≒ 65nm CMOS process (1.8V analog transistors) ≒ 0.14mm2 active area per channel ≒ Voltage supplies: High voltage rail 賊1.4V Low voltage rail 賊0.35V ≒ Switching point 50mV under the low voltage supply ≒ Max load capacitance 1nF 17/28
  • 23. 23 Measurement results: Power dissipation versus output power Fin=1kHz RL=32立 18/28
  • 24. Measurement results: THD+N and efficiency versus output power ≒Sinusoidal input signal (fin=1kHz) ≒About 6dB extra distortion due to switching 19/28
  • 25. Performance summary and comparison with literature Parameter This work (Class G) JSSC 09 (Class AB) [1] ESSCIRC 06 (Class AB) [2] ISCAS 09 (Class D) [3] Technology 65nm 130nm 65nm 0.13um Supply voltage 賊1.4V 賊0.35V 賊1V 賊0.6V 2.5V 3.6V Quiescent power (per channel) 0.41mW 1.2mW 12.5mW 1.8mW Peak load power (16立) 90mW 40mW 53.5mW 50mW THD+N @ PRMS (32立) -80dB @ 16mW -84dB @ 10mW -68dB @ 27mW (16立) -80dB @ 10mW SNR A-weighted 101dB 92dB (un- weighted) - 96dB [1] Vijay Dhanasekaran, JSCC 09 [2] P. Bogner, ESSCIRC 06 [3] Pillonet, ISCAS 09 20/28
  • 26. Performance comparison with products Parameter This work (Class G) MAX9725 (Class AB) TPA6141 (Class G) LM48824 (Class G) Supply voltage 1.4V with two charge pumps + 1 buck 1.5V with one charge pump 3.6V with 1 charge pump + 1 buck 3.6V with 1 charge pump + 1 buck Quiescent power (per channel) 0.41mW + 0.3mW (2 CPs + 1 buck) 1.57mW 2.16mW 1.62mW PSUP @ PL=0.1mW 0.87mW + 0.4mW - 4.5mW 3.24mW PSUP @ PL=0.5mW 1.63mW + 0.6mW - 7.2mW 5.58mW Peak load power (16立) 90mW 70mW (CPs RON=2.5立) 50mW 50mW 74mW THD+N @ PRMS (32立) -80dB @ 16mW -84dB @12mW -80dB @20mW -69dB@20mW SNR A-weighted 101dB 92dB 105dB 102dB 21/28
  • 27. Outline ≒ Headphone amplifier (Class-AB, Class-D, Class-G PROs and CONs) ≒ Class-G headphone driver (architecture, switching principle, distortion analysis) ≒ Prototype in 65nm CMOS technology (implementation, results, comparison) ≒ Class G improved version (new SNR Spec, proposed solution, results and comparison) ≒ Conclusions
  • 28. New Spec: increase the SNR of 10dB 3-stages improved performance Aim: increase the SNR Classical approach: increase gM1 and consequently CM1 ISCC 10 3-stages improved SNR @ 1VRMS 100dB 110dB CM1 15pF 260pF CM2 4x18pF 4x18pF PQ 0.41mW 0.55mW Big area where 22/28
  • 29. 4-stages Feed Forward (FF) solution ≒ The additional stages increase the open loop gain of the amplifier at low frequencies ≒ The stage gM11 dominates the noise performance Additional stages Ref: A. Bosi et all. VDSL2 Analog Front End, ISSCC, 2009 23/28
  • 30. 4-stages Feed Forward (FF) solution ≒ The amplifier cuf off frequency is gM1/CM1 ≒ The GLOOP shows a zero at Low freq path High freq path High freq path gM1 Low freq path gM11/sC 揃 gM12 24/28
  • 31. 4-stages FF: GLOOP plot 4-stages FF solution: 1. gM11 determines the noise performances 2. More open-loop gain in the audio BW Audio BW (20Hz-20kHz) 25/28
  • 32. 4-stages FF: Less capacitors sizes 3-stages improved performance: 4-stages FF: gM11 determines the noise performance Big area Audio BW (20Hz-20kHz) 26/28
  • 33. 4-stages FF: Less switching distortion 4-stages FF shows higher switching distortion compression We can reduce gM2 saving power consumption We can reduce CM2 saving area 3-stages: 4-stages FF: 3-stages 4-stages FF gM2 200uA/V 55uA/V CM2 4x18pF 4x5pF THD@1kHz -82dB -85dB We saved additional 52pF Switching distortion Switching distortion 27/28
  • 34. Performance summary ISCC 10 3-stages improved 4-stages FF SNR@1VRMS 100dB 110dB 110dB CTOT 87pF 332pF 101pF PQ 0.41mW 0.55mW 0.6mW THD@1kHz -82dB -82dB -85dB Conclusion: The adopted solution shows the same performance as the 3-stages one using 1/3 of total capacitors area paying only 10% of additional power consumption. 28/28
  • 35. Outline ≒ Headphone amplifier (Class-AB, Class-D, Class-G PROs and CONs) ≒ Class-G headphone driver (architecture, switching principle, distortion analysis) ≒ Prototype in 65nm CMOS technology (implementation, results, comparison) ≒ Conclusions
  • 36. Conclusions ≒ A class-G headphone driver has been presented. It shows 50% less power consumption than the best competitor. ≒ The class-G improved version satisfies the most aggressive market requirements (110dB of SNR and better than 80dB of THD) ≒ The class-G improved version will be integrated in Dec 2010 into a novel Marvell audio codec
  • 37. Publications ≒ Marvell Patent Ref No. MP3391: A. Lollio, G. Bollati, R. Castello, CIRCUITS AND METHODS FOR AMPLIFYING SIGNALS ≒ A. Lollio, G. Bollati, R. Castello, Class-G Headphone Driver in 65nm CMOS Technology, Proc. ISSCC 2010, San Francisco, 7-11 Feb. 2010, pp.84-85 ≒ A. Lollio, G. Bollati, R. Castello, A Class-G Headphone Amplifier in 65nm CMOS Technology IEEE J. Solid-State Circuits, vol. 45, no. 12, Dec. 2010.
  • 38. Activities Summary Seminari organizzati dal dottorato (3.8 CFU) Scuole di Dottorato (12 CFU) Corso Elementi di Elettronica di Potenza (5 CFU) Corso di Misure Elettriche (5 CFU) Tutorato di Elettronica (2 CFU) Presentazione a Congresso Internazionale: ISSCC2010 (3 CFU) Pubblicazione su rivista internazionale: JSSC2010 (4 CFU) Presentazioni annuale sullattivit di ricerca svolta (1.5 CFU) Totale CFU: 36.3
  • 39. Buck and CPs: Power consumption estimation (per channel) 2 Charge pumps PQ -> 0.2mW 1 Buck (80% efficiency), PL=0 Pdiss -> 0.1mW 1 Buck (80% efficiency), PL=0.1mW Pdiss -> 0.2mW 1 Buck (80% efficiency), PL=0.5mW Pdiss -> 0.4mW Total power consumption PQ -> 0.2mW+0.1mW = 0.3mW PL=0.1mW -> 0.2mW+0.2mW = 0.4mW PL=0.5mW -> 0.2mW+0.4mW = 0.6mW
  • 40. Measurement results: THD+N versus frequency RL=32立 BW= 20Hz 20 kHz
  • 41. 41 Measurement results: Spectrum at different output power PO=20mW Fin=1kHz PO=1mW Fin=1kHz
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