Motorola 8900 User Manual - Page 50

Audio Interface Figure 2-15 shows the microphone circuit and Table 2-6 gives the microphone specifications. Figure 2-15: Handset Microphone Circuit Important: The 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 microphone port specifications. Table 2-6: Handset Microphone Port Specifications Parameter Conditions Min Typ Max Unit Input Voltage No load Gain Programmable by 9 AT Command AC Input Impedance Freq=1Khz Bias voltage Bias Current RBIAS = 2.2 kΩ IBIAS < 1 mA 1.6 Vpp 36 dB 1 kΩ 1.8 V 1 mA Headset Microphone Port The headset microphone port is designed for use with, but not limited to, a headset audio device. It is located at pin 57 on the C24 interface connector, named HDST_MIC. It is designed as a single-ended input and should be referenced to the C24 analog ground. 26 C24 Module Hardware Description December 15, 2008