Motorola 8900 User Manual - Page 51

Chapter 2: Hardware Interface Description The microphone input includes all the necessary circuitry to support a direct connection to a headset microphone device. It incorporates an internal bias voltage of 1.8V through a 2.2kΩ resistor, and has an impedance of 1kΩ. Figure 2-16 shows the microphone circuit and Table 2-7 gives the microphone specifications. Figure 2-16: Headset Microphone Circuit Important: The headset microphone circuit design depends on the type of microphone device. A series capacitor is required in case a passive microphone is used, or the application provides a separate bias voltage to an active microphone circuit. The internal C24 biasing circuit may also be used with an active microphone, which corresponds to the headset microphone port specifications. Table 2-7: Headset Microphone Port Specifications Parameter Conditions Min Typ Max Unit Input Voltage No load Gain AC Input Impedance Bias voltage Bias Current Programmable by 9 AT Command Freq=1Khz RBIAS = 2.2 kΩ IBIAS < 1 mA 1.6 Vpp 36 dB 1 kΩ 1.8 V 1 mA Speaker Port The analog speaker port is the C24 power-up default active output for voice calls and DTMF tones. It is located at pins 67 and 69 on the C24 interface connector, named SPKR_N and SPKR_P respectively. December 15, 2008 C24 Module Hardware Description 27