Design Goal Design an Analog-to-Digital Conversion chip to meet demands of high quality voice applications such as: Digital Telephony, Digital Hearing Aids and VOIP. TEAM W3: Digital Voice Processor 525 Jarrett Avery (W3-1) Sean Baker (W3-2) Huiyi Lim (W3-3) Huiyi Lim (W3-3) Sherif Morcos (W3-4) Amar Sharma (W3-5) Date: 2/1/2006 Architecture Proposal

Status  Design Proposal  Project chosen: 16 bit Delta-Sigma ADC  Basic specs defined  Architecture  Matlab Simulated  Behavioral Verilog – Done, but not simulated  Schematic  Floorplanning  Layout  Simulation / Verification

In Case You Forgot… (A Summary of Last Week) Applications of the DVP-525 Applications of the DVP-525 VoIP, Digital Telephony, Encrypted Communications VoIP, Digital Telephony, Encrypted Communications Digital Hearing Aids Digital Hearing Aids How the DVP-525 works: How the DVP-525 works: Uses Delta-Sigma modulation of input signal and decimation to convert an analog signal into 16 bit binary numbers Uses Delta-Sigma modulation of input signal and decimation to convert an analog signal into 16 bit binary numbers

Algorithm Detail Decimation (Sinc Filter, Downsample) Measure Peak Amplitude (Peak Input Indicator) Digital Output Digital Peak Indicator Analog Input Lowpass Filter Analog to Digital Conversion (Delta-Sigma Modulator)

Hardware That Makes it Happen (Modulator) Integrators Comparator

Algorithm Detail Decimation (Sinc Filter, Downsample) Measure Peak Amplitude (Peak Input Indicator) Digital Output Digital Peak Indicator Analog Input Lowpass Filter Analog to Digital Conversion (Delta-Sigma Modulator)

Hardware That Makes it Happen (Decimator) These accumulators and registers are clocked at the sampling frequency: (Nyquist Clock * 256) These differencers and registers are clocked at the Nyquist rate

Algorithm Detail Decimation (Sinc Filter, Downsample) Measure Peak Amplitude (Peak Input Indicator) Digital Output Digital Peak Indicator Analog Input Lowpass Filter Analog to Digital Conversion (Delta-Sigma Modulator)

Hardware That Makes it Happen (Peak Input Indicator)

Important Concepts for Delta- Sigma ADCs Oversampling Oversampling Nyquist Frequency – minimum frequency for reconstruction of signal Nyquist Frequency – minimum frequency for reconstruction of signal OSR – Oversampling Ratio, f S / f N OSR – Oversampling Ratio, f S / f N Oversampling spreads out noise spectrum Oversampling spreads out noise spectrum For 2 nd order modulator, signal to noise ratio (SNR) increases by 15dB (32x higher) for each doubling of OSR For 2 nd order modulator, signal to noise ratio (SNR) increases by 15dB (32x higher) for each doubling of OSR

Effects of Oversampling f S = f N f S = f N * OSR Band of Interest Diminished Noise Band of Interest Noise freq amplitude

More Important Concepts Noise Shaping Noise Shaping Integrator in feed-forward path and DAC in feedback path pushes noise out of signal bandwidth Integrator in feed-forward path and DAC in feedback path pushes noise out of signal bandwidth

Transistor Estimate Analog Analog 3 x Analog Op Amps, 3 x 24 = 72 3 x Analog Op Amps, 3 x 24 = 72 Capacitive Resistive Elements Capacitive Resistive Elements Digital Digital 8 x 18 bit registers, 8 x 250 = x 18 bit registers, 8 x 250 = x 18 bit adders, 6 x 500 = x 18 bit adders, 6 x 500 = x 18 bit comparators, 2 x 800 = x 18 bit comparators, 2 x 800 = x 24 bit counter, 1 x 1000 = x 24 bit counter, 1 x 1000 = x 24 bit comparator, 1 x 1000 = x 24 bit comparator, 1 x 1000 = x 18 bit muxes, 4 x 150 = x 18 bit muxes, 4 x 150 = 600 Misc logic = 200 Misc logic = 200 Total Transistors = 9,472 Total Transistors = 9,472

Simulation First modeled the modulator in the time domain, and fed it a simple sine wave input: First modeled the modulator in the time domain, and fed it a simple sine wave input:

Simulation (cont’d) Then fed the bitstream created by the modulator into the decimator: Then fed the bitstream created by the modulator into the decimator:

Design Decisions Chose 2 nd order Delta-Sigma Modulator Chose 2 nd order Delta-Sigma Modulator Eases speed requirements (lower OSR) Eases speed requirements (lower OSR) Makes digital logic simpler Makes digital logic simpler Stability issues won’t be crippling Stability issues won’t be crippling Chose Sinc3 filter for decimation Chose Sinc3 filter for decimation For Lth order modulator, need L+1 order Sinc filter For Lth order modulator, need L+1 order Sinc filter Not a perfect LPF, but pretty good & economical Not a perfect LPF, but pretty good & economical Bandwidth of interest – 20 Hz to 10 KHz Bandwidth of interest – 20 Hz to 10 KHz Focuses on voice applications, but doesn’t limit product Focuses on voice applications, but doesn’t limit product Decided on OSR of 256 Decided on OSR of 256 Gives 16 effective bits of resolution Gives 16 effective bits of resolution Makes sampling frequency 256*(10 KHz * 2) = 5.12 MHz Makes sampling frequency 256*(10 KHz * 2) = 5.12 MHz Optional digital function: Peak Input Indicator (PII) Optional digital function: Peak Input Indicator (PII) Holds value of highest and lowest amplitude (refreshes every few seconds) Holds value of highest and lowest amplitude (refreshes every few seconds) Could be used to prevent blowing out speakers, etc. Could be used to prevent blowing out speakers, etc.

Problems and Questions Is the decimation filter enough for the digital section of the project? Is the decimation filter enough for the digital section of the project? Use higher order sinc filter, faster adders? Use higher order sinc filter, faster adders? Include PII? Include PII? Input 2 clock signals to the decimator, or input 1 clock and generate the 2 nd from the 1 st ? Input 2 clock signals to the decimator, or input 1 clock and generate the 2 nd from the 1 st ? Analog Issues Analog Issues How fast do the op-amps need to run (settling time, stability, etc.) How fast do the op-amps need to run (settling time, stability, etc.) What gain is required of op-amps? What gain is required of op-amps? Active or passive Butterworth filter for the input? Active or passive Butterworth filter for the input? Input voltage levels? Pre-amplification? Input voltage levels? Pre-amplification?

Results More comfortable with overall design More comfortable with overall design A lot of this is new to us… A lot of this is new to us… We have a marketable product We have a marketable product Ready to move forward with design Ready to move forward with design Gate level verilog for the digital parts Gate level verilog for the digital parts Topology, gate sizing, RLC selection for analog parts Topology, gate sizing, RLC selection for analog parts