TDMA T2290/T2297:
Audio Circuit
B30
Description
When a headset is in serted in J940, the internal speaker an d microphone is dis abled. The user can now use the headset for handsfree conversation. BOOM_MIC_DET
informs U1000 whethe r a headset is inse rted or not. The state of BOOM_MIC_DET is controlled by Q1 551.
When the headset is inserted the biasing voltage for the AUX_MIC will no longer be pr esent at the base of the NPN transistor Q1551. This will switch Q1551 on, thus,
allowing BOOM_MIC_DE T to be pulled high by source 2.75V. When the headset is not inserted, the AUX_MIC biasing voltage is present at the base of Q1551. This
condition will switch Q1551 off, thus, pulling the BOOM_MIC_DET to ground through R1540.
There are two distinct audio paths for the microphone. One is for the auxilia ry microphone(headset mic) and the other is for the internal micr ophone. This is not the case
with the speaker audio paths. The headset speaker and the int ernal speaker share the same audio path which comes from the GCAP(U1500). In order to disable th e inter-
nal speaker when the headset is attached, the phase of the audio signal on the SPKR- line is phase shifted by 180 º. When the internal speaker is enabled the SPKR+ and
SPKR- have the same audio signal e xcept that SPKR- is phase shifted 1 80º. When a headset is attached, the SPKR- is not phase shifted 180º . The SPKR+ and SPKR-
have the same audio signal and are in phase. This condition will no t allow the internal s peaker to function, thus, disabling the inte rnal speaker.
J940
HDST_ SPKR
AUX_MIC
Q1551
BOOM_MIC_DET
Headset Speaker
Headset Mic
2.75V
R1540
Содержание T2290
Страница 1: ...DIGITAL WIRELESS TELEPHONE Service Manual Level 3 Release 1 TDMA T2290 T2297 ...
Страница 26: ... 2000 Motorola Inc TDMA T2290 T2297 Cellular Overview 16 ...
Страница 40: ...Motorola Confidential Proprietary TDMA T2290 T2297 TDMA Test Mode NAM Programming 30 ...
Страница 68: ...Disassembly TDMA T2290 T2297 Keypad Removal Motorola Confidential Proprietary 58 ...