Programmable analog array and EMG signal acquisition and application of

Introduction

In biological signal acquisition, signal amplitude as a result of the measured object, different kinds of biological potential of the spectrum, the different muscle groups as well as skin electrodes coupling, and other factors vary, so typically you need depending on the measured object adjustment analog front-end amplifiers magnification and bandwidth.

Implementation of such regulation of one possible option is to use programmable analog array (FPAA), through the use of programmable analog array implements a RMS-DC converters or to zoom in on EMG (electromyography) signal digital and microprocessor processing RMS values. FPAA let all analog circuit required in a programmable component implementation, it ensures greater flexibility and reliability of the system, and reduce the size of the circuit and reduce costs.

The EMG signal processing, a front-end using analog circuit complete benefits is that the EMG signal collection rates range from 10 μ v to 1 mV, these signals need to zoom to 60-100dB, therefore, the use of a high common-mode rejection ratio (CMRR) integrated instrumentation amplifier can minimize the impact of common mode interference.

Filter level using analog circuit, when the band frequency needs further decay time, usually the second or fourth-order low-pass and high pass filter.

This article describes the use of EMG signals Anadigm FPAA on for collection and disposal of circuit design, the analog signal processing project purpose is to obtain from EMG signal sufficient biological characteristics, to control such as artificial limbs or electric Stimulator for external devices.

Characteristics of FPAA

As programmable gate array (FPGA) is a digital circuit design change, FPAA to analog circuit design introduces a convenient prototyping methods and reducing design time.

In FPAA most important unit is configurable analog modules (CAB), which subtly to deal with a variety of signals and the routed network. FPAA is a can be programming and again programming integrated circuit, analog circuit function can perform routing-end adjustments. Circuit configuration files from the PC, system controller or incidental EEPROM download-FPAA, resulting in functional integrity of the circuit. The circuit configuration variable at any time, for a completed feature configuration can be changed in the new download or real-time upgrade to reconfigure.

Based on a switched-capacitor technology by Anadigm AN221E04 FPAA have configurable properties of a number of CAB, and can be programmed to perform different functions, such as filter, amplifier, multiplier, comparator, and other features.

These features can be used in a biological signal acquisition and processing. In addition, FPAA interrupted the CMRR amplifier is 102dB, thus bringing the common mode interference signal and power cables jamming 60Hz.

Circuit description

Circuit realization use AnadigmDesigner 2 software, which includes circuit simulator and a programmable devices, use the AN220D04 evaluation board serial interface on the work test.

Battery evaluation board using optical interface is connected to a computer to ensure patient safety.

The system of the block diagram shown in Figure 1.

Figure 1 for EMG signal acquisition and processing system block diagram

For EMG signal acquisition

Through the acquisition of the surface electrode EMG signal amplitude in 10 μ v to 1 mV range, however, the common mode signal (interference) may be as high as a few volts.

Researchers had previously recommended several technologies to FPAA and other analog circuit interface, however, they are not suitable for biological potential of the acquisition, therefore, researchers presented a new configuration, where the reference electrodes are connected to the reference pin FPAA (VMRR), while the active electrode is directly connected to the intermittent input.

Intermittent amplifier is used to zoom in with the DC component, very small and very low frequency signal, the signal from amplifier bias.

For EMG, 10Hz following it has negligible, however, it is provided by FPAA analog front-end options provide better acquisition results.

The source of interference is minimized through the use of masking technique, use a shorter cable, prevent ground loops, in electrode area ready to be logging the skin as well as using Paste Ag-AgCl electrode.

These measures allow for the acquisition of sufficient signal to noise ratio, the simulation domain for continuous signal processing.

Analog signal filtering

EMG signal bandwidth is defined as from 50 Hz to 350 Hz.

As a design option, you can use the low order filter configured to signal to noise ratio in enough to capture the EMG signal. This is the use of a second order Chebyshev band-pass filter and a bilinear filters, therefore, the low-frequency attenuation for every ten octaves higher than 20dB, on frequency attenuation of bandwidth every ten octaves 40dB.

Input level use is configured to have 64 intermittent amplifier gain.

The first filter level is the center frequency to 200Hz, 5 gain bandwidth 300Hz of band-pass filter; the second level is a cutoff frequency for 500Hz, gain 20 low-pass filter. Signal conditioning circuits total gain to 6400 (76dB). All parameters can be reconfigured at any time.

Acquisition of transfer functions such as circuit equations 1 and 2, they represent the intermittent input level, biquadratic bandpass filter, lowpass filters with double linear transfer function.

Of these, GChop

Per is intermittent amplifier gain; GBP is a bandpass filter's gain; GLP is a low-pass filter gain; fBP is band-pass filter frequency; the center of the fLP is a low-pass filter cutoff frequency; Q is a bandpass filter quality factor.

As shown in Figure 2 as Equation 1 frequency response, the drawing is to use the signal generator (HP 33120A) access, and in 2 software AnadigmDesigner simulation drawn from Matlab.

Visible from the figure, the theory and experimental results similar to the difference between the derived from experimental error or FPAA circuit of tolerance. The simulation also demonstrated FPAA development tools is reliable.

Figure 2 frequency response map: solid as Matlab simulation results; (□) cable to the simulation and experimental AnadigmDesigner 2 results

RMS value of

RMS value of certainty is done using classic topology.

Multiplication and square root extraction is the use of the CAB FPAA. Outside of a RC was used as a first order filter, is directly connected to the FPAA difference output and once again injected into the same FPAA, as shown in Figure 3.

Figure 3 using analog circuit produces RMS value of classic topology

Use from volunteers of the biceps acquisition of EMG signals as well as using Paste Ag-AgCl electrode so that with low ripple RMS signal, at the same time, ensure that the response time of the circuit, as shown in Figure 4.

RC in the experiment can be regulated, the final value is R = 220 k and C = 470 nF, defined cutoff frequency for 1.5Hz.

Figure 4 RMS value (Channel 2: 500 mV/div) and the biceps signal (Channel 1: 1 V/div)

Analog signal processing last level by trigger pulses in comparators circuit or – when the EMG RMS level adjusted set point threshold — to control external devices switch control circuit.

FPAA circuit has a variable reference the comparer to perform this function, and the reference voltage as sensitivity thresholds.

Complete electric circuit as shown in Figure 5.

In Figure 5 on the top right corner of the output 3 and 4 correspond to the amplifier and filter the square of EMG signals, while the lower-right corner of the output 7 and 8 corresponds to the analog signal processing after EMG signal RMS.

Figure 5 is used to capture the complete EMG signal FPAA circuit

FPAA circuit (AN221E04) high common-mode rejection ratio allows for high common-mode noise suppression capabilities for very small amounts of biological EMF (10 μ μ v to 500 V) acquisition.

Next, by using interference minimization techniques produce low-noise signal, the signal can be enough quality to be used as a prosthetics or electrical stimulation for the control signal.

The above examples, programmable analog array has the flexibility to modify the characteristics of analog circuits, such as the use of software to modify the filter cutoff frequency, gain, reference voltage and can be modified during the work of the circuit, therefore, FPAA will help quickly and reliably achieve medical electronic systems design analog front-end prototype.

Programmability of the development trend

Large-scale field-programmable analog array (FPAA) in simulation area has great potential for development.

Industry experts said that the benefits of FPAA is: 1. Simulation of pretreatment can alleviate A/D converter existing bottlenecks and reduce DSP operations after the level of burden; 2. FPAA has significant potential to reduce small analog circuit design prototype creation time, to meet the requirements of large arrays, which can be one of the most comprehensive instrument simulation applications or even provide adequate performance; 3. Compared with the DSP programmes, the main advantage of FPAA is the entire power consumption than FPAA single ADC module also low; 4. compared with the full custom ASIC's main advantage is the flexibility and faster design, development and deployment cycle.

However, this technique also need FPAA continue to solve many problems.

For example, due to the alignment and switch increases the noise limits the analog circuit performance, and reduce the signal to noise ratio. However, industry experts think, FPAA technology over time and become more mature, and hopefully bring a simulation design revolution. At present, companies such as Anadigm and Lattice programmable analog array is available.

In addition, TI and linglier principal companies based on a spreadsheet of filter design program.

Currently, the available online analog filter design program with the United States national power filter design tools (Active Filter Designer), with the help of this tool is a convenient way for Bezier, Bart, Chebyshev or Gaussian filter properties to select high-pass or low pass filter parameters, these programmable analog application design tool, but also will provide medical electronic systems design of analog front end provides greater flexibility.

Reference documents:

1. the programmability in small signal measurement systems, electronic products, http://www.eepw.com.cn/article/85904.htm

2. http://www.anadigm.com/

3. programmable system-core

The design of a framework for the electronic design technology, EDN article.ednchina.com/EDA/20061203110239.htm

4.

FPAA chip AN10E40 and its applications, worry-free electronic development network, www.51kaifa.com/html/jswz/200512/read-4138.htm