| 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. |
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 |
|
| High Gain to amplify signals prior to A/D conversion |
|
| Band Pass Filter to remove out of band noise |
|
| Low Power for ambulatory (portable) applications |
|
| High Resolution A/D Conversion |
|
| Custom Logic to combine digital ExG streams |
|
| Serial Communication to transfer digitized electrode data to a host computer for display |
|
| Reduced Development NRE
Reduced Development Time |
|
| Reduced Risk |
|
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:
- Sampling frequency is adjustable by changing the ASIC master clock and/or through SPI control to change the clock generator divider ratio.
- 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.
