LME49720 DECT Cordless Phone EMI Susceptibility
Posted: Sat Feb 17, 2018 4:15 pm
Myself and some contributors at DIY Audio have noticed that the LME49720 and its variants are prone to EMI from DECT cordless phone base stations 100 Hz polling.
The following test circuit is low impedance (1-2 KΩ range) unity gain circuitry 8 feet from a DECT base station. Also nearby were a 4G phone, the DECT handsets, a WiFi access point and wireless weather instruments. The circuit board temporarily sits in a grounded metal tin. I removed the lid to illustrate the effect. The line frequency in these parts is 60 Hz.
To improve the FFT of the LME49720, only the DECT base station needed to be turned off.
The comparisons are similar when the LME49720 is compared to NE5532s, NJM2114s and other popular duals.
No other dual op amp I tested exhibited this rectification.
EMI Susceptibility of OPA2134 vs LME49720 No DECT Base Station
The LME49720 is slightly quieter in the above owing to its lower voltage noise.
When the DECT 6.0 base station is turned on all hell breaks loose in the LME49720 channel...
EMI Susceptibility of OPA2134 vs LME49720 DECT Base Station Powered
DECT transmits a "dummy bearer" signal to the headset every 10 ms.
The LME49720 exhibits rectification of the 100 Hz pulsed carrier.
I wanted to get this documented.
Your milage may vary.
The following test circuit is low impedance (1-2 KΩ range) unity gain circuitry 8 feet from a DECT base station. Also nearby were a 4G phone, the DECT handsets, a WiFi access point and wireless weather instruments. The circuit board temporarily sits in a grounded metal tin. I removed the lid to illustrate the effect. The line frequency in these parts is 60 Hz.
To improve the FFT of the LME49720, only the DECT base station needed to be turned off.
The comparisons are similar when the LME49720 is compared to NE5532s, NJM2114s and other popular duals.
No other dual op amp I tested exhibited this rectification.
EMI Susceptibility of OPA2134 vs LME49720 No DECT Base Station
The LME49720 is slightly quieter in the above owing to its lower voltage noise.
When the DECT 6.0 base station is turned on all hell breaks loose in the LME49720 channel...
EMI Susceptibility of OPA2134 vs LME49720 DECT Base Station Powered
DECT transmits a "dummy bearer" signal to the headset every 10 ms.
The LME49720 exhibits rectification of the 100 Hz pulsed carrier.
I wanted to get this documented.
Your milage may vary.