ECE 5540 Homework 2

Mini project: design audio driver with noise cancellation

Overview: You will design circuit to drive audio-band signals onto a speaker while monitoring the output with a microphone to provide distortion correction and noise (interference) cancellation. You will be provided with a model of speaker, microphone, and supporting electronics. Your job is to design a transistor-level circuit to meet the below specs while minimizing DC power consumption and silicon area.

Model description: You will be supplied with two blocks to model interfaces of the circuit. All other components in your final design must come from the 6hp library: you may use off-chip ideal resistors and capacitors, but each one will be considered equal to 1 mm2 of layout area . The speaker is a coil driving a fixed magnet attached to a membrane, with an impedance of approximately 8. The Microphone is a membrane with a fixed charge suspended above a gate-less FET, modulating its resistance, which we will just model as a voltage source with thevenin resistance of 1k. Finally the signal source is centered at Vref (which you must generate) and swings up to +/- 150mV with a 10k output impedance. VDD models the battery/charger power supply. The audio-peripherals model (Audio_model) includes a 2-terminal input port for the speaker (speaker_p, speaker_m), a 2-terminal output port for the microphone (MIC_p, MIC_m), and a 1-terminal (ground-referenced) output (audio_out) whose voltage models the output sound-wave. The model includes modeling of impedance, transfer functions, and external audio noise to be suppressed. The electronics model (sys_model) includes the signal source (ground-referenced) which supplies the desired audio signal (sig),centered on the voltage you provide to ref, gnd and vdd modelling a battery. This also includes a model of VDD ripple when charging.

Specifications: To be met across temperature (-20C to 80C), process, and supply (1.3V

Suggestions/Hints:

1) Characterize the Speaker/MIC model, finding the input impedance across frequency, as well as the transfer function from speaker to MIC and Audio_out. Also characterize the magnitude of external noise (interference) that needs to be suppressed.

2) You will need to design a feedback circuit from microphone to speaker to compensate for gain variation and suppress noise: compute a first estimate of the required transfer function.

3) Design an idealized block diagram first, and spec out your sub-circuits. Test and refine this design using idealized amplifiers (voltage-controlled voltage sources (vcvs), etc) and components (res, cap, etc) from analogLib. Confirm you meet specs with these ideal models.

4) Now, start with lego-style designs to get functionality, gain and stability, then refine for noise, efficiency and drive strength.

5) Design under nominal conditions (T=26C, VDD=1.5V, process=tt) but with 3-6dB margin. Once you meet this, verify for corners and refine, improving if you fail a spec, trimming current if you still have significant margin in all cases (2dB or more).

Deliverables:

1) Interim report (1 for whole group, due Feb 25th by email): 2 pages or 2 slides showing: a. A block diagram of your approach (at the level of amplifier stages, etc) and computed

specs for the sub-circuits (Gain, bandwidth, input-referred noise) b. First-draft schematics of sub-circuits. c. Simulation results showing function and non-awful results (within 20dB of specs) under

nominal conditions. 2) Final report (1 for whole group due March 5th): 5 pages showing:

a. A ~ 1 page 1.5-spaced text (12 point) narrative of your design process. b. Block diagram of your approach and computed specs for the sub-circuits (This may be

the same as the interim report if nothing has changed) c. Fully annotated schematics of top-level and sub-circuits. d. Filled out specification table across corners. e. Screen shots of most marginal simulation results (ie plot of worst-case noise, SFDR, etc

across temperature, process, etc) with annotation. f. Layout of components (unrouted) with rulers showing superscripted rectangular area. g. A 1 to 1.5-page discussion of most interesting/difficult aspect of the design, supported

by 1-2 figures. Also discuss what parts of the circuit/system limit your performance (noise, distortion, power consumption).

h. References to any resources you used. 3) Summary slide (1 for group due March 5th) to be posted for other groups edification showing:

a. Group-members names (I will strip these before posting) b. Annotated Block diagram c. 3 sentence description of approach d. Results table e. Figure showing most important/interesting circuit/technique/insight with 2 sentence

description f. References

4) Design files (1 for group) of all schematics, layout, etc. due March 5th 5) Cross-evaluation (one per group member, to be emailed to me directly due March 6th):

a. 1 paragraph review of group dynamics b. Percent contribution of each group member, including yourself, totaling 100%.

Interim report template:

Group members names

1 paragraph text overview

Description of block diagram, and critical specs of sub-circuits

Brief description of circuits and simulation plots.

Block Diagram

Annotated circuit schematics

Specification summary table:

Specification Simulated result

Min/max gain from 20Hz-20kHz

Integrated output noise, V

Peak output noise V/Hz1/2

SFDR (in dBV)

DC current from VDD (IDD), A

Area, in m2

Brief description of plan going forward

Annotated simulation plots: Gain vs frequency, output noise, plots of transient signal on Speaker,

microphone and Audio_out. FFT of Audio_out.

Final report template:

Group members names

Narrative: 1 page

Description of block diagram, and specs of sub-circuits

Brief text describing schematics

Block Diagram

Annotated circuit schematics, including top-level, and any subcircuits.

This may cove more than one page

Spec. name Nom. -20C 100C SS FF 1.3 VDD 1.8VDD 100C, SS -20C, FF

Max Gain, dB

Min Gain, dB

Int. noise, V

Max noise V/Hz

SFDR, dBV

Start-up/stable (Y/N)

IDD, mA

Area,

Simulation plots of worst-case scenarios

Worst case AC gain Worst case Noise

Worst case SFDR (FFT of Audio out) Worst-case start-up (transient

Example transient on Speaker, MIC Worst case transient on Audio_out

Discussion (with two figures)

References:

(not required, but if you use external resources, you must reference them)

Annotated layout