Im using ADS1294R for ECG acquisition and have designed my own harware for the same. Our development is almost complete. ECG and respiration is working fine without any problem.The only issue now is Pacer detection.We followed the hardware pacer detection approach as mentioned in the datasheet.But whenever the pacer detection amplifier of ADS1294R is switched ON , some stray frequency components(pereodic) are obtained as output from TESTP_PACE1 & TESTN_PACE2 pins which are falsely triggering my pacer detection hardware(even when the pacer pulses are not given by the simulator).When i was going through the datasheet of the chip, i could see that there is a positive feedback for pace amplifier(ADS1298-Page No: 69). What is the significance of that??Or is it a printing miatake?I need an urgent reply since this is the only issue and my development is in halt because of this.I cannot implement software pace detection because of my datarate requirement which cant be changed(500SPS) Im using channels 2&3 (Lead 1 & Lead 2) as the analog out from ADS.My register settings are :
void ads_config(void)
{
send_SPI(0x41); //LP 500SPS
__delay_us(2);
send_SPI(0x00);
send_SPI(0x05); //500sps
__delay_ms(1);
send_SPI(0x42);
__delay_us(2);
send_SPI(0x00);
send_SPI(0x11);
__delay_ms(1);
send_SPI(0x43);
__delay_us(2);
send_SPI(0x00);
send_SPI(0xCE);
__delay_ms(1);
send_SPI(0x44);
__delay_us(2);
send_SPI(0x00);
send_SPI(0x17);
__delay_ms(1);
send_SPI(0x45);
__delay_us(2);
send_SPI(0x03);
send_SPI(0x05);
send_SPI(0x05);
send_SPI(0x05);
send_SPI(0x05);
__delay_ms(1);
send_SPI(0x4d);
__delay_us(2);
send_SPI(0x01);
send_SPI(0x0E);
send_SPI(0x02);
/*send_SPI(0x4f);
__delay_us(2);
send_SPI(0x01);
send_SPI(0x0f);
//__delay_us(2);
send_SPI(0x0f);*/
__delay_ms(1);
send_SPI(0x51);
__delay_us(2);
send_SPI(0x00);
send_SPI(0x00);
__delay_ms(1);
send_SPI(0x54);
__delay_us(2);
send_SPI(0x00);
send_SPI(0x00);
__delay_ms(1);
send_SPI(0x55);
__delay_us(2);
send_SPI(0x00);
send_SPI(0x03);
__delay_ms(1);
send_SPI(0x56);
__delay_us(2);
send_SPI(0x00);
send_SPI(0xe6);
__delay_ms(1);
send_SPI(0x57);
__delay_us(2);
send_SPI(0x00);
send_SPI(0x22);
__delay_ms(1);
send_SPI(0x58);
__delay_us(2);
send_SPI(0x00);
send_SPI(0x10);
__delay_ms(1);
send_SPI(0x59);
__delay_us(2);
send_SPI(0x00);
send_SPI(0xE3);
__delay_ms(1);
initially im using the test signal for som calibration and after that within 4ms im changing the channel configuration to 0x00(PGA gain = 6) ; I have tried switching OFF the internal test signals completely when Pacer is ON. I have tried powering down WCT amplifiers and DC Lead off detection to veryfy what is the source of the pereodic noise comin from the analog out pins.Even if i switch OFF the simulator,the response is same..If the Pacer amplifier is ON, the signal is there (even if no simulator input).Pacer ampl OFF,there is no issue.But nothing helped. First i want to clarify whether the positive feedback for PACE amplifiers as mentioned in the internal diagram in the datasheet is a printing mistake or not.if not what is the significance? Is there any application note or other documents discussing pacer detection with the ADS AFE chips? Please reply.
