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Digital-to-Analog Converters (DACs)

Requirements

  • Looking for > 18 bit (equal or better to the VS1053b)
  • 2 channels for stereo audio
  • Low power consumption for better battery life
  • Low unit price

I confess that I don’t know enough to set constraints for performance and characteristics beyong bit-depth, such as dynamic range, total harmonic distortion, noise, integral/derivative nonlinearity. (2) provides a very good reference for understanding DAC performance metrics. I’ll be using this space to take notes from that document.

Architecture

DAC Architectures consist of three main types: R-2R, delta-sigma, and string. According to (2), delta-sigma (aka noise shaping or one-bit) DACs are used in lower cost-applications compared to R-2R.

R-2R have a higher theoretical noise limit compared to

Summary Table

See Appendix for extended notes on parts |DAC |Bit-depth (bits)|Dynamic Range (dB)|THD+N (dB)|Input Voltage (V)|Power (mW)|Price (USD)|Package| |——–|———|————-|——–|————-|——–|—–|——-| |CS4338 |24|96|-88|5|75|1.95-2.51|8-SOIC | |CS43L41 |24|101|-89|2.4-5|24|2.00|16TSSOP| |CS4329 |20|106|-97|5|22.5|5.98|20 DIP | |CS4360 |24|102|-91|3.3|116|5.14-6.35|28TSSOP| |AD1934 |24|108|-94|3.3|429|8.86|48LQFP |

Thoughts

CS43L41 provides the best price-performance with comparable characteristics to the higher end DACs at half the price and possessing close to the lowest power consumption of any of the DACs. If I am to design multiple versions of the same board, I would use the CS43L41 and potentially experiment with the AD1934 to test the effect of the better characteristics on audio quality.

Additionally, the CS43L41 provides volume control and line level outputs, obviating the need for additional output amplification. The reference design is extremely simple to implement, with only an optional mute circuit and filtering.

Analog-to-Digital Converters (ADCs)

I am debating whether or not to include an analog or digital mixer for the optional 1/4” TRS passthrough for my bass. With digital, I would need a preamp and an ADC to convert the signal from my bass to digital audio, then the DSP can perform mixing and perhaps even apply effects to the bass. This seems overly ambitious, perhaps I should make it an optional module: a separate board with a 1/4” TRS jack, preamp, voltage regulators, and voltage reference, which can be connected to the MCU with SPI communication. To reduce future work, I’ll go through selecting an ADC now (just in case).

Requirements

MCU/Dev Boards

I will most likely choose to integrate an MCU directly or use an existing dev board (e.g. RP Pico 1&2, ESP32, STM32 Blue pill). Using the dev boards allows me to directly utilize their existing bluetooth/WiFi capabilities. This saves me both the headache of designing my own board for the MCU and lets me get away with not having to solder QFN packages.

Raspberry Pi Pico 1 W (RP2350)

I’ll be doing my first version with a RPi Pico 1W because that’s what I already have. I will be programming it using C/C++

Appendix

DAC Selection

Cirrus Logic CS433(4/8)

Price: $1.95 - 2.51

  • 24 bit, 96 kHz
  • 2 channel
  • 5V analog & digital supply, 75 mW
  • 96 dB Dynamic Range
  • -88 dB THD+N
Cirrus Logic CS43L41

Price: $2.00

  • 24 bit, 96 kHz
  • 2 channel
  • 2.4V-5V analog & digital supply, 24 mW @ 2.4V
  • 101 dB Dynamic Range
  • -89 dB THD+N
Cirrus Logic CS4329

Price: $5.98 Specs:

  • 20 bit, 32, 44.1, and 48 kHz sampling rate
  • Delta Sigma Architecture
  • 2 channels
  • 5V analog & digital supply, 22.5 mW
  • 106 dB Dynamic Range
  • 115 dB SNR
  • -97 dB THD+N
Cirrus Logic CS4360

Price: $5.14 Specs:

  • 24 bit, 192 kHz
  • Delta Sigma Architecture
  • 6 channel
  • 3.3V analog & digital supply, 116 mW
  • 102 dB Dynamic Range
  • 115 dB SNR
  • -91 dB THD+N
Analog Devices AD1934 (WBSTZ)

Price: $8.86 Specs:

  • 24 bit, 192 kHz
  • Delta Sigma Architecture
  • 8 channel
  • 3.3V analog & digital supply, 429 mW
  • 108 dB Dynamic Range
  • 108 dB SNR
  • -94 dB THD+N
Analog Devices AD5680 nanoDAC

Price $10.74 Specs:

  • 18 bit (12 bit accuracy guaranteed???)
  • Single 5V supply @ 1.6 mW
  • -80 dB THD

Citations

  1. “A DAC for all precision occasions” (https://www.ti.com/lit/an/slyt300/slyt300.pdf)
  2. “DYNAMIC PERFORMANCE TESTING OF DIGITAL AUDIO D/A CONVERTERS” (https://www.ti.com/lit/an/sbaa055/sbaa055.pdf)
  3. “Line Level” (https://en.wikipedia.org/wiki/Line_level)