AD8232-EVALZ

AD8232-EVALZ Datasheet

AD8232 EVALUATION BOARD DOCUMENTATION

Part	Datasheet
AD8232-EVALZ	AD8232-EVALZ (pdf)

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One Technology Way • P.O. Box 9106 • Norwood, MA 02062-9106 • Tel • Fax • AD8232 EVALUATION BOARD DOCUMENTATION q Ready to use Heart Rate Monitor HRM Front end q Accepts 2 or 3 electrode options q Directly interface to data acquisition or ADC q Access features with switch jumpers q Allows various circuit configurations Figure The AD8232-EVALZ contains an AD8232 Heart Rate Monitor Front End conveniently mounted with the necessary components for initial evaluation in fitness applications. Inputs, outputs, supplies and other circuit test points have been routed to vector pins to simplify connectivity to test clips and probes. Switches and jumpers are available for setting the input common-mode, shutdown SDN , fast-restore FR , and AC/DC leads-off detection. QUICK START The board ships with a default configuration for three-electrode systems connected to the hands. Ensure that the switches and jumpers are set to the default values shown in Table For two-electrode configurations, the settings are shown in Table TABLE Quick Start Switch Settings FUNCTION LABEL CONFIGURATION Shutdown P1 Enabled Fast Restore P2 Enabled AC/DC Leads Detection P5 DC method enabled 5V Input P4 5V input LDO disabled Input pull-up voltage J2 Pull up inputs to +VS Note that the 5V LDO may not be installed on all boards Figure Default Board Settings Connect the power supply common to the GND terminal on the board. Connect a positive supply voltage between 3V and 3.3V to the +VS terminal. Connect the input electrodes to the +VIN and terminals. The right-leg drive is available via the RLD terminal. Connect this terminal to the subject with a third electrode. The output signal is available on the VOUT terminal and it may be connected to a scope or ADC. Note that the electrode interfaces +VIN, -VIN and RLD are equipped with 180kΩ and 499kΩ R6, R7 and R1 respectively resistors to limit current injection to the subject in the event of fault or overload. Please note that these will not protect against supply line transients coming through the system. Isolation from the power line is always required when connecting to a live subject. It is recommended to fully understand common safety practices the proper application of such guidelines is sole responsibility of the end user. DEFAULT CIRCUIT CONFIGURATION Signal Path Inamp and Filters The evaluation board ships with a default configuration for applications that involve three-electrodes connected at the hands. The terminals +VIN, and RLD serve as the inputs and right-leg drive electrode connections respectively. The instrumentation amplifier has a fixed gain of 100 and the op-amp is set for a gain of The overall gain is 1100V/V, which limits the maximum differential input signal to about 2.7mVp-p. Exceeding this amplitude will not damage the AD8232, but the signal at the output will appear distorted. Due to the filter’s high-Q, there is additional peaking that sets the maximum observed gain above 1100V/V around 15Hz. The total gain may be changed by adjusting the resistors R12 and R13, but this will have a direct impact on the Q of the low-pass filter. Note that the instrumentation amplifier has a fixed gain of A single-supply is used to implement the entire signal chain. For this purpose, the reference buffer is set to a ratiometric level at mid-supply using two 10MΩ resistors R8 and R10 . The integrated reference buffer output provides a virtual ground level to allow high-pass filtering. The signal at the output will ride on top of this mid-supply level. This voltage is available at the REFOUT pin to serve as a zero level for subsequent signal-acquisition stages. The circuit implements a two-pole high pass filter for eliminating motion artifacts and the electrode half-cell potential. Additionally, the integrated operational amplifier creates a two-pole low pass filter to remove line noise and other interference signals. The frequency cutoff of all filters may be changed by adjusting component values. A complete version of the schematic and a section summarizing the explanation of the components can be found at the end of this document. Figure AD8232-CHARZ Board Simplified Schematic Refer to Figure 12 for complete version Right-Leg Drive Amplifier The integrated right-leg drive RLD amplifier senses the common mode voltage present at the signal inputs and can drive an opposing signal into the patient. This driven electrode functionality maintains the voltage between the patient and the AD8232 constant, greatly improving the common mode rejection ratio. The board configures the RLD amplifier as an integrator, formed by an internal 150kΩ resistor and an external capacitor of 1nF C1 . This results in a loop gain of about 20 at line frequencies, with a crossover frequency of about 1 kHz. In a two-lead configuration, the RLD pin can be used to drive the bias current resistors on the inputs. To create this connection, place a jumper on J3. FILTER DESIGN The resistor and capacitor values for the filters were selected to provide effective noise rejection in applications that involve pulse detection while the subject is in motion. The filter parameters can be adjusted to fit other applications. High-Pass Filters The instrumentation amplifier in the AD8232 applies gain and high pass filtering simultaneously. This capability allows it to amplify a small ECG signal by 100 while rejecting electrode offsets as large as ±300 mV. The cutoff frequency of this filter is given by the following equation fc = 100 / R9 C6 In this particular case, R9= 10MΩ and C6 = 0.22uF place the pole of the first high-pass at 7Hz. Note that the filter cutoff is 100 times higher than would be typically expected, because of the feedback architecture of the instrumentation amplifier. Figure Frequency response In-Amp filter dc blocking feature An ac-coupling network C9 and R11 at the output of the instrumentation amplifier introduces a second pole. The cutoff frequency is that of a regular passive first-order high-pass filter fc = 1 / R11 C9 This results in a 7Hz cutoff frequency for 0.22uF and 100kΩ. Both high-pass filters together yield a total roll-off of 40dB per decade. Be aware that setting the same pole location for both high-pass filters will result in 6dB attenuation at the corner frequency. In addition, because the output of this filter is unbuffered, the instrumentation amplifier exhibits higher output impedance at the input of the

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One Technology Way
• P.O. Box 9106
• Norwood, MA 02062-9106
• Tel
• Fax
•

AD8232 EVALUATION BOARD DOCUMENTATION
q Ready to use Heart Rate Monitor HRM Front end q Accepts 2 or 3 electrode options q Directly interface to data acquisition or ADC q Access features with switch jumpers q Allows various circuit configurations

Figure

The AD8232-EVALZ contains an AD8232 Heart Rate Monitor Front End conveniently mounted with the necessary components for initial evaluation in fitness applications. Inputs, outputs, supplies and other circuit test points have been routed to vector pins to simplify connectivity to test clips and probes. Switches and jumpers are available for setting the input common-mode, shutdown SDN , fast-restore

FR , and AC/DC leads-off detection.

QUICK START

The board ships with a default configuration for three-electrode systems connected to the hands. Ensure that the switches and jumpers are set to the default values shown in Table For two-electrode configurations, the settings are shown in Table

TABLE Quick Start Switch Settings

FUNCTION

LABEL CONFIGURATION

Shutdown

P1 Enabled

Fast Restore

P2 Enabled

AC/DC Leads Detection P5 DC method enabled
5V Input

P4 5V input LDO disabled

Input pull-up voltage J2

Pull up inputs to +VS

Note that the 5V LDO may not be installed on all boards

Figure Default Board Settings

Connect the power supply common to the GND terminal on the board. Connect a positive supply voltage between 3V and 3.3V to the +VS terminal.

Connect the input electrodes to the +VIN and terminals. The right-leg drive is available via the RLD terminal. Connect this terminal to the subject with a
third electrode. The output signal is available on the VOUT terminal and it may be connected to a scope or ADC.

Note that the electrode interfaces +VIN, -VIN and RLD are equipped with 180kΩ and 499kΩ R6, R7 and R1 respectively resistors to limit current injection to the subject in the event of fault or overload. Please note that these will not protect against supply line transients coming through the system. Isolation from the power line is always required when connecting to a live subject. It is recommended to fully understand common safety practices the proper application of such guidelines is sole responsibility of the end user.

DEFAULT CIRCUIT CONFIGURATION

Signal Path Inamp and Filters

The evaluation board ships with a default configuration for applications that involve three-electrodes connected at the hands. The terminals +VIN, and RLD serve as the inputs and right-leg drive electrode connections respectively.

The instrumentation amplifier has a fixed gain of 100 and the op-amp is set for a gain of The overall gain is 1100V/V, which limits the maximum differential input signal to about 2.7mVp-p. Exceeding this amplitude will not damage the AD8232, but the signal at the output will appear distorted. Due to the filter’s high-Q, there is additional peaking that sets the maximum observed gain above 1100V/V around 15Hz. The total gain may be changed by adjusting the resistors R12 and R13, but this will have a direct impact on the Q of the low-pass filter. Note that the instrumentation amplifier has a fixed gain of

A single-supply is used to implement the entire signal chain. For this purpose, the reference buffer is set to a ratiometric level at mid-supply using two 10MΩ resistors R8 and R10 . The integrated reference buffer output provides a virtual ground level to allow high-pass filtering. The signal at the output will ride on top of this mid-supply level. This voltage is available at the REFOUT pin to serve as a zero level for subsequent signal-acquisition stages.

The circuit implements a two-pole high pass filter for eliminating motion artifacts and the electrode half-cell potential. Additionally, the integrated operational amplifier creates a two-pole low pass filter to remove line noise and other interference signals. The frequency cutoff of all filters may be changed by adjusting component values.

A complete version of the schematic and a section summarizing the explanation of the components can be found at the end of this document.

Figure AD8232-CHARZ Board Simplified Schematic Refer to Figure 12 for complete version

Right-Leg Drive Amplifier

The integrated right-leg drive RLD amplifier senses the common mode voltage present at the signal inputs and can drive an opposing signal into the patient. This driven electrode functionality maintains the voltage between the patient and the AD8232 constant, greatly improving the common mode rejection ratio. The board configures the RLD amplifier as an integrator, formed by an internal 150kΩ resistor and an external capacitor of 1nF C1 . This results in a loop gain of about 20 at line frequencies, with a crossover frequency of about 1 kHz. In a two-lead configuration, the RLD pin can be used to drive the bias current resistors on the inputs. To create this connection, place a jumper on J3.

FILTER DESIGN

The resistor and capacitor values for the filters were selected to provide effective noise rejection in applications that involve pulse detection while the subject is in motion. The filter parameters can be adjusted to fit other applications.

High-Pass Filters

The instrumentation amplifier in the AD8232 applies gain and high pass filtering simultaneously. This capability allows it to amplify a small ECG signal by 100 while rejecting electrode offsets as large as ±300 mV. The cutoff frequency of this filter is given by the following equation fc = 100 / R9 C6 In this particular case, R9= 10MΩ and C6 = 0.22uF place the pole of the first high-pass at 7Hz. Note that the filter cutoff is 100 times higher than would be typically expected, because of the feedback architecture of the instrumentation amplifier.

Figure Frequency response In-Amp filter dc blocking feature An ac-coupling network C9 and R11 at the output of the instrumentation amplifier introduces a second pole. The cutoff frequency is that of a regular passive first-order high-pass filter fc = 1 / R11 C9 This results in a 7Hz cutoff frequency for 0.22uF and 100kΩ. Both high-pass filters together yield a total roll-off of 40dB per decade. Be aware that setting the same pole location for both high-pass filters will result in 6dB attenuation at the corner frequency. In addition, because the output of this filter is unbuffered, the instrumentation amplifier exhibits higher output impedance at the input of the

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Datasheet ID: AD8232-EVALZ 517751