Bioelectric Amplifiers

Market: Medical
Target Platform: VCA-4
Application: Bioelectric Amplifiers used in EEG, ECG, and EMG applications to amplify and digitize multi-channel electrodes to monitor brain, heart, and muscle activity.
Figure 1

Bioelectric amplifiers are used in EEG, ECG, and EMG applications like those shown Figure 1. These systems are used to measure electrical signals from the brain (EEG), heart (ECG/EKG), and muscles in general (EMG). A typical system can have from 1 to 256 sensor channels. The electrodes detect small electrical signals which require large amounts of gain and filtering to extract the information in the presence large common mode noise.

Many EEG/ECG/EMG systems are implemented as ‘boxes’ containing discrete analog circuitry to amplify and filter each sensor channel. Systems can have up to 256 channels and manufacturers are looking for:

  • Integration – reduce size and weight to support portable applications
  • Cost Reduction – reduce overall cost per electrode channel to support systems with up to 256 channels
  • Power Savings – required for portable applications

Triad has ASIC building blocks, domain expertise in bioelectric amplifier circuit design, and existing VCA platforms optimized for the bioelectric amplifier marketplace.

Triad VCA Building Blocks for Bioelectric Amplifier Applications

Bioelectric Amplifier System Requirements
Triad VCA Building Blocks
Low Noise
  • Low Power Low Noise Op-Amp
  • 2uVp-p input referred noise
  • Correlated Double Sampling Amplifiers
High Gain to amplify signals prior to A/D conversion
  • Programmable Gain Amplifiers
Band Pass Filter to remove out of band noise
  • Continuous Time, Switched Capacitor Filters
  • Switched Capacitor Filters
  • Digital Decimation Filters
Low Power for ambulatory (portable) applications
  • Low Power Analog Tiles
  • Low Power Band Gap
  • Low Power Digital with Sleep Mode Power Savings
High Resolution A/D Conversion
  • 16-bit Sigma Delta ADC
  • Fully Differential Architecture
  • 2nd, 3rd, 4th – order modulators
Custom Logic to combine digital ExG streams
  • 24K Configurable ASIC Gates
  • 48Kbits of Embedded SRAM
Serial Communication to transfer digitized electrode data to a host computer for display
  • SPI
  • IIC
  • USB
Reduced Development NREReduced Development Time
  • Single Mask to configure a custom ASIC
  • Support for 4-channel EEG, EKG, EMG System
  • Single Mask Fabrication Time – 4 Weeks
  • No Full-Custom Layout Required
  • Accelerate Development with Triad Proven IP
Reduced Risk
  • Triad has domain expertise in bioelectric amplifier design and Triad engineers are available to take your idea to full-production.
  • Triad engineers have developed over 130 successful ASICs.
  • 10+ years of experience per Triad Engineer

4-Channel Bioelectric Amplifier Triad VCA ASIC

Utilizing the VCA-4 platform a 4-channel bioelectric amplifier can be realized as shown in Figure 2 below. This ASIC provides the following features:

  • 4-channel Bioelectric Sensor Data Acquisition
  • Low-Noise Input Stage: 2uVp-p input referred noise
  • Input Stage Gain: 30dB
  • Digitally Programmable Gain Stage: -5dB to +30dB
  • Each channels gain independently settable via SPI commands
  • 16-bit Sigma Delta Fully Differential Analog to Digital Converter
  • Digital Decimation Filter & Stream Combiner with Serial Output
  • SPI Control Interface (optionally IIC or UART)
  • Package: 40-lead QFN, 6mm x 6mm

Symbol

Parameter

Conditions

Min

Typ

Max

Units

Resolution

16

Bits
fS Sampling Frequency(1)

2

KHz
INL Integral Nonlinearity

-0.5

+0.5

LSB
DNL Differential Nonlinearity

-0.5

+0.5

LSB
IRVN Input Referred Voltage Noise 0.1 to 100Hz

2.0

μVp-p
PSRR Power Supply Rejection Ratio

90

dB
CMRR Common Mode Rejection Ratio

110

dB
Ch Channels 16-bit sensor channels on the VCA-4 platform

4

fC LPF cut off frequency(2)

500

Hz
VDD Power Supply Range

3.0

3.3

3.6

Volts
IDD Power Supply Current Per channel

0.5

mA

Notes:

  1. Sampling frequency is adjustable by changing the ASIC master clock and/or through SPI control to change the clock generator divider ratio.
  2. LPF Anti-aliasing filter cutoff frequency may be changed by changing the ASIC master clock or via SPI control. Additionally, alternative filter topologies can be implemented by schematic-only circuit changes which will require only a single mask fabrication change to the ASIC.
Figure 2