9.2.1 3-Lead ECG Application
In the 3-Lead ECG example shown in Figure 84, the right-arm (RA), left-arm (LA), left-leg (LL) and right-leg (RL) electrodes are connected to the IN1, IN2, IN3 and IN4 pins. The ADS1293 uses the Common-Mode Detector to measure the common-mode of the system by averaging the voltage of input pins IN1, IN2 and IN3, and uses this signal in the right-leg drive feedback circuit
. The output of the RLD amplifier is connected to RL through IN4 to drive the common-mode of the system. The chip uses an external 4.096-MHz crystal oscillator connected between the XTAL1 and XTAL2 pins to create the clock source for the device.
9.2.1.1 Design Requirements
For this design example, use the parameters listed in Table 12 as the set-up parameters.
Table 12. Design Parameters
DESIGN PARAMETER |
EXAMPLE VALUE |
Number of electrodes |
4 |
Lead I definition |
LA – RA |
Lead II definition |
LL –RA |
Bandwidth |
175 Hz |
Output data rate |
853 sps |
Analog supply voltage |
5.0 V |
Digital I/O supply voltage |
3.3 V |
9.2.1.2 Detailed Design Procedure
Follow the next steps to configure the device for this example, starting from default registers values.
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Set address 0x01 = 0x11: Connect channel 1’s INP to IN2 and INN to IN1.
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Set address 0x02 = 0x19: Connect channel 2’s INP to IN3 and INN to IN1.
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Set address 0x0A = 0x07: Enable the common-mode detector on input pins IN1, IN2 and IN3.
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Set address 0x0C = 0x04: Connect the output of the RLD amplifier internally to pin IN4.
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Set address 0x12 = 0x04: Use external crystal and feed the internal oscillator's output to the digital.
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Set address 0x14 = 0x24: Shuts down unused channel 3’s signal path.
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Set address 0x21 = 0x02: Configures the R2 decimation rate as 5 for all channels.
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Set address 0x22 = 0x02: Configures the R3 decimation rate as 6 for channel 1.
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Set address 0x23 = 0x02: Configures the R3 decimation rate as 6 for channel 2.
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Set address 0x27 = 0x08: Configures the DRDYB source to channel 1 ECG (or fastest channel).
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Set address 0x2F = 0x30: Enables channel 1 ECG and channel 2 ECG for loop read-back mode.
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Set address 0x00 = 0x01: Starts data conversion.
Follow the description in the Streaming section to read the data. The ADS1293 will measure lead I and lead II. Lead III can be calculated as follows: Lead III = Lead II – Lead I
Optionally, the third channel could be used to measure Lead III.
9.2.1.3 Application Curves
Figure 85 show measurement data collected by a single ADS1293 device connected to an ECG simulator configured to produce an ECG signals at a rate of 60 per minute and with an amplitude of 2 mV. The data was collected simultaneously by channels 1 and 2 of the device during a period of 10 seconds.
9.2.2 5-Lead ECG Application
In the 5-Lead ECG example shown in Figure 86, the ADS1293 uses the Common-Mode Detector to measure the common-mode of the system by averaging the voltage of input pins IN1, IN2 and IN3, and uses this signal in the right-leg drive feedback circuit
. The output of the RLD amplifier is connected to RL through IN4 to drive the common-mode of the system. The Wilson Central Terminal is generated by the ADS1293 and is used as a reference to measure the chest electrode, V1. The chip uses an external 4.096 MHz crystal oscillator connected between the XTAL1 and XTAL2 pins to create the clock source for the device.
9.2.2.1 Design Requirements
For this design example, use the parameters listed in Table 13 as the setup parameters.
Table 13. Design Parameters
DESIGN PARAMETER |
EXAMPLE VALUE |
Number of electrodes |
5 |
Lead I definition |
LA – RA |
Lead II definition |
LL –RA |
Lead V definition |
V1 – WCT |
Bandwidth |
175 Hz |
Output data rate |
853 sps |
Analog supply voltage |
5.0 V |
Digital I/O supply voltage |
3.3 V |
9.2.2.2 Detailed Design Procedure
The following steps configure the ADS1293 for a 5-lead application with an ECG bandwidth of 175 Hz and an output data rate of 853 Hz; it is assumed that the device registers contain their default power-up values.
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Set address 0x01 = 0x11: Connects channel 1’s INP to IN2 and INN to IN1.
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Set address 0x02 = 0x19: Connect channel 2’s INP to IN3 and INN to IN1.
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Set address 0x03 = 0x2E: Connects channel 3’s INP to IN5 and INN to IN6.
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Set address 0x0A = 0x07: Enables the common-mode detector on input pins IN1, IN2 and IN3.
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Set address 0x0C = 0x04: Connects the output of the RLD amplifier internally to pin IN4.
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Set addresses 0x0D = 0x01, 0x0E = 0x02, 0x0F = 0x03: Connects the first buffer of the Wilson reference to the IN1 pin, the second buffer to the IN2 pin, and the third buffer to the IN3 pin.
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Set address 0x10 = 0x01: Connects the output of the Wilson reference internally to IN6.
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Set address 0x12 = 0x04: Uses external crystal and feeds the output of the internal oscillator module to the digital.
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Set address 0x21 = 0x02: Configures the R2 decimation rate as 5 for all channels.
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Set address 0x22 = 0x02: Configures the R3 decimation rate as 6 for channel 1.
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Set address 0x23 = 0x02: Configures the R3 decimation rate as 6 for channel 2.
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Set address 0x24 = 0x02: Configures the R3 decimation rate as 6 for channel 3.
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Set address 0x27 = 0x08: Configures the DRDYB source to ECG channel 1 (or fastest channel).
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Set address 0x2F = 0x70: Enables ECG channel 1, ECG channel 2, and ECG channel 3 for loop read-back mode.
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Set address 0x00 = 0x01: Starts data conversion.
Follow the description in the Streaming section to read the data.
9.2.2.3 Application Curves
Figure 87 show measurement data collected by a single ADS1293 device connected to an ECG simulator configured to produce an ECG signals at a rate of 60 per minute and with an amplitude of 2 mV. The data was collected simultaneously by channels 1, 2 and 3 of the device during a period of 10 seconds.
9.2.3 8- or 12-Lead ECG Application
Figure 88 shows the ADS1293 master/slave setup for an 8-Lead to 12-Lead ECG system. The ADS1293 uses the Common-Mode Detector to measure the common-mode of the system by averaging the voltage of input pins IN1, IN2 and IN3, and uses this signal in the right-leg drive feedback circuit
. The output of the RLD amplifier is connected to the right-leg electrode to drive the common-mode of the system. The Wilson Central Terminal is generated by the ADS1293 and is used as a reference to measure the chest electrodes, V1-V6; TI strongly recommends shielding the external Wilson connections, which due to the high output impedance of the Wilson reference, is prone to pick up external interference. The master ADS1293 generates a synchronization pulse on the SYNCB pin (configured as an output). This drives the SYNCB pins (configured as inputs) of the two slave ADS1293. The master chip uses an external 4.096 MHz crystal oscillator connected between the XTAL1 and XTAL2 pins to create the clock source for the device and outputs this clock on the CLK pin.
9.2.3.1 Design Requirements
For this design example, use the parameters listed in Table 14 as the setup parameters.
Table 14. Design Parameters
DESIGN PARAMETER |
EXAMPLE VALUE |
Number of electrodes |
10 |
Lead I definition |
LA – RA |
Lead II definition |
LL –RA |
Lead V1 definition |
V1 – WCT |
Lead V2 definition |
V2 – WCT |
Lead V3 definition |
V3 – WCT |
Lead V4 definition |
V4 – WCT |
Lead V5 definition |
V5 – WCT |
Lead V6 definition |
V6 – WCT |
Bandwidth |
175 Hz |
Output data rate |
853 sps |
Analog supply voltage |
5.0 V |
Digital I/O supply voltage |
3.3 V |
9.2.3.2 Detailed Design Procedure
The next steps will configure the master device; it is assumed that the device registers contain their default power-up values.
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Set address 0x01 = 0x11: Connects channel 1’s INP to IN2 and INN to IN1.
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Set address 0x02 = 0x19: Connect channel 2’s INP to IN3 and INN to IN1.
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Set address 0x0A = 0x07: Enables the common-mode detector on input pins IN1, IN2 and IN3.
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Set address 0x0C = 0x04: Connects the output of the RLD amplifier internally to pin IN4.
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Set addresses 0x0D = 0x01, 0x0E = 0x02, 0x0F = 0x03: Connects the first buffer of the Wilson reference to the IN1 pin, the second buffer to the IN2 pin, and the third buffer to the IN3 pin.
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Set address 0x12 = 0x05: Uses external crystal, feeds the output of the internal oscillator module to the digital, and enables the CLK pin output driver
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Set address 0x14 = 0x24: Shuts down unused channel 3’s signal path.
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Set address 0x21 = 0x02: Configures the R2 decimation rate as 5 for all channels.
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Set address 0x22 = 0x02: Configures the R3 decimation rate as 6 for channel 1.
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Set address 0x23 = 0x02: Configures the R3 decimation rate as 6 for channel 2.
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Set address 0x27 = 0x08: Configures the data-ready source to channel 1 ECG (or fastest channel).
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Set address 0x28 = 0x08: Configures the synchronization source to channel 1 ECG (or slowest channel).
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Set address 0x2F = 0x30: Enables ECG channel 1 and ECG channel 2 for loop read-back mode.
Next, configure the slave devices; it is assumed that the device registers contain their default power-up values. In this example, both devices will have the same configuration; therefore, they can potentially be configured in parallel by asserting the CSB signal of both chips.
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Set address 0x01 = 0x0C: Connects channel 1’s INP to IN1 and INN to IN4.
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Set address 0x02 = 0x14: Connects channel 2’s INP to IN2 and INN to IN4.
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Set address 0x03 = 0x1C: Connects channel 3’s INP to IN3 and INN to IN4.
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Set address 0x12 = 0x06: Uses external clock signal on the CLK pin and feeds it to the digital.
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Set address 0x21 = 0x02: Configures the R2 decimation rate as 5 for all channels.
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Set address 0x22 = 0x02: Configures the R3 decimation rate as 6 for channel 1.
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Set address 0x23 = 0x02: Configures the R3 decimation rate as 6 for channel 2.
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Set address 0x24 = 0x02: Configures the R3 decimation rate as 6 for channel 3.
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Set address 0x27 = 0x00: DRDYB pin not asserted by slave devices.
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Set address 0x28 = 0x40: Disables SYNCB driver and configures pin as input.
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Set address 0x2F = 0x70: Enables ECG channel 1, ECG channel 2, and ECG channel 3 for loop read-back mode.
Finally, start the conversion. This should be written to all three chips.
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Set address 0x00 = 0x01: Starts data conversion (repeat this step for every device).
The three devices will run synchronously using the SYNCB signal. Follow the description in the Streaming section to read the data. The ADS1293 measures lead I, lead II and leads V1-V6. For a 12-lead application, the remaining 4 leads can be calculated as follows:
- Lead III = Lead II – Lead I
- aVR = – ( I + II ) / 2
- aVL = I – II / 2
- aVF = II – I / 2
9.2.3.3 Application Curves
Figure 89 show measurement data collected by 3 synchronized ADS1293 devices connected to an ECG simulator configured to produce an ECG signals at a rate of 60 per minute with an amplitude of 2 mV. The data was collected simultaneously by multiple channels from all 3 devices during a period of 10 seconds.