Motorola P8190 Service Manual download pdf (Page 100)

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P8190: Antenna Circuit

Antenna

EXT_ANT

Q702

TX_2.75

U700

U701-A

U701-B

Q700

U704

800MHz

1900MHz

FL453

Not used

1900MHz

FL453

Not used

Description

Two RF ports are designed in this transceiver; internal antenna and external antenna. The RF switch(U704) controls which antenna path is going to be used during operation.

U704 has two control inputs which are used to control the RF routing.

The internal antenna will be used only when there is no load at the EXT_ANT port. The absence of a load at the EXT_ANT port will not bias the base of PNP transistor Q702

on. This condition will not allow TX_2.75 to be present at one of the inputs of the exclusive OR gate U700.

When a load is present at the EXT_ANT port, the base of Q702 is biased. This condition will switch Q702 off, allowing the input of U700 to be in a low state.

U700 only has one output which allows only two possible states, high or low. With this in consideration, U704 will also have only to possible states.

The states of U704 are determined by the output of U700. A low state at the output of U700 will switch Q700 on. This condition will pull the input the inverter U701-A low.

The output of U701-A will provide a high state at V2. U701-B is then used to invert the state and provide a low state at V1. Having a low state at the output of U700 will

invert all the states.

Having a high state at V2 and a low state at V1 will configure U704 to route the EXT_ANT port to the 800MHz RF path.

A low state at V2 and a high state at V1 will configure U704 to route the antenna port to the 800MHz RF path.

Only one RF port is used at a time, therefore, only one RF switch configuration is used while the other is irrevelent.