Suitable comparator circuit headset detection


Posted on Mar 28, 2007

Headphone type detection circuit according to the figure attached. Figure, 2.2k RMIC-BIAS resistor connected to the audio controller provides a low noise reference voltage (VMIC-REF). When the audio jack is inserted, VMIC-REF voltage through RMIC-BIAS


Suitable comparator circuit headset detection
Click here to download the full size of the above Circuit.

is applied to the plug - equivalent resistance (not shown) on the ground, so the MAX9063 in the noninverting input of a voltage VDETECT. For stereo headphones, the resistance is small (8, 16, or 32 ); for the microphone, the current source current because of the absorption of fixed types of different microphones in 100 A to about 800 A between floating and thus the resistance value is large. Since VDETECT headphones into the jack with the type of change, it is possible to monitor VDETECT by a comparator to determine the type of headset. As shown, assume microcontroller reference voltage (VMIC-REF) is 3V, 32 headphone load produces VDETECT voltage of 43mV. The fixed current 500 A microphone load, a voltage of 1.9V. Note that most applications will have problems VDETECT direct connection. Given the typical microcontroller port CMOS input logic level is higher than the requirements of 0.7 VCC and lower than 0.3 VCC, then 3.3V supply microcontroller input logic level should be higher than 2.3V, less than 1V. 1.9V level 500 A microphone load generated is not a valid logic "1" level. 100 A to 800 A microphone bias current will generate 2.78V to 1.24V for VDETECT, any voltage drops below 2.3V violates the controllers VIH (input high, assuming RBIAS to 2.2k ) requirements. In order to obtain higher voltage or 2.3V, the microphone bias current must be 318 A or less. Otherwise we will have to change the 2.2k bias resistor, thereby changing the microphone detection threshold. Because of the typical load of 32 headphones can easily pull the level close to ground, thus generating a logic low of 1V or less easy to implement. In order to detect the type of headset, you need to VDETECT connected to one input of the comparator, the reference voltage is connected to the other input. The comparator output, which represents the type of headset. This portable headset detect application should have a small size, and low power consumption. Shown comparator measuring just 1mm 1mm, maximum supply current of only 1 A. It has a strong mobile phone frequency anti-jamming capability, providing high reliability. The comparator also has internal hysteresis and low input bias current and other characteristics. These features make it to space, power consumption is extremely sensitive battery-powered products (such as: mobile phones, portable media players and laptops) an ideal choice for headset detection circuit.




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