Specification for microphone input
First stage in the CD949 microphone path is an active microphone. This is
needed to get a good signal to noise ration on the long cable between
microphone and CD949 radio unit. The electrical specification for the
microphone (according VDA) could be seen in the table below.
1. 8V Biasvoltage
2. only two Pins
3. 10 k minimum load
4. at P=74dB,1 khz and 30cm distance it has to deliver 190 mVPP
with a distortion of less then 1%
5. more then 15 dB dynamic range
6. Flat frequency response from 300 Hz to 4 khz +– 1 dB
7. signal to Noise ratio of more then 50 dB at 1% distortion limit
8. mountable on sunscreen and at chassis of the Car
9. Possibility to drive 7m microphone cable
To interface this microphone, the CD949 radio unit has a low noise power
supply The input stage of CD949 has to have an input impedance of >20