Tait TP9100 Service Manual

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Contents

TP9100 Service Manual Circuit Descriptions 63© Tait Electronics Limited May 2005Audio Signalfor Speaker The audio signal for the speaker is generated by IC204 (VOUTAUXP ball).This signal is post-volume-control decoupled by C238 and fed to the audiopower amplifier.Audio PowerAmplifier The signal from C238 is fed to the audio power amplifier IC200. IC200 has22dB of gain and a differential output configuration. Gain is configured bythe resistors R260 and R259. When operational, the output bias voltage forIC200 is approximately half the radio supply voltage. When not operational,the output becomes high impedance.Control of AudioPower Amplifier Power up, power down, and muting of IC200 is controlled by one signalfrom the digital section, DIG AUD PA EN. The network consisting of Q200,R254 and R256 converts the digital signal to the single three-level analogsignal required by IC200. A “pop-free” audio PA on/off control is activatedby a fast transition on the MODE pin of IC 200.Control of InternalSpeaker Audio The differential signal to the internal speaker can be disconnected by dual-MOSFET IC207, under control of the digital signal DIG INT SPK INH.The external speaker audio signal is permanently connected to the outputof IC200.Microphone Signals There are two microphone source signals:■ ACC MIC AUD from accessory connector■ internal speaker as a microphoneThe biasing for electret microphones is provided by a filtered 3.0V supplyvia R226. The components R209 and C202 provide the supply filtering.The microphone inputs to IC204 (VINAUXP, VINAUXN, VINNORP and VINNORNballs) are differential. The negative inputs are decoupled to the filtered 3.0Vsupply by C215 and C216. The positive input of ACC MIC AUD is biased toapproximately 1.5V by R229 and R232. AC coupling and DC inputprotection is provided by C213.The microphone signal from the internal speaker is converted fromdifferential to single/ended by IC202 and then fed to VINNORP ball of IC204as the internal microphone signal.Accessory AudioInput The accessory audio input signal ACC AUD TAP IN is DC-coupled to the ADCinput of IC205. R241 combined with internal clamping diodes in IC205provide DC protection for the ADC input. IC205 provides the input biasingof approximately 1.5 V.