PMB2208 查看數據表（PDF） - Infineon Technologies

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PMB2208

Mixer and IF Vector Modulator

Infineon Technologies 

Confidential

PMB 2208

preliminary

Functional Description

3.5 Circuit Description

The modulator performs a direct quadrature modulation. The LO signal is con-

nected to an emitter-coupled transistor pair. The LO signal is split internally into

two orthogonal carriers at half of the LO/LOX input frequency. The accuracy of

the internal 90° phase shift requires a balanced input signal and depends on the

accuracy of the 50% duty cycle of the LO/LOX signal. The modulator has two

Gilbert cell mixers, in which the baseband modulation signals at the A/AX and

B/BX inputs are multiplied with the orthogonal carriers. The outputs of the two

Gilbert cells are added and amplified by a linear output stage. The modulated

transmit signal is available at the high-impedance, open-collector output E/EX.

It can be band-pass filtered and fed to the IF/IFX input of the mixer.

At the TREF output, a reference voltage is available, which should be capaci-

tively decoupled to ground. TREF can be used to set the DC bias of the base-

band inputs using external resistors. Alternatively, the DC level can be set

independently of TREF, provided it is within the specified operational range.

The up/down-conversion mixer is a fully-balanced Gilbert cell. The transfer

function from the low-impedance emitter input IF/IFX to the output is linear for

input levels below the 1dB compression point. For improved intermodulation,

the mixer current can be increased with external resistors to ground at IF/IFX.

The high-impedance input RF/RFX is directly connected to the bases of the

switching transistors. The input level should be high enough to ensure proper

switching. The output signal of the mixer is available at the high-impedance,

open-collector outputs MO/MOX.

The modulator and the mixer have separate supply and power-down pins:

VCC1, PD1 for the modulator and VCC2, PD2 for the mixer. Applying a logic

LOW to PD1 or PD2 powers down the corresponding part of the chip, including

its bias circuitry. Depending on the application, the power-down pins can be

combined or separately fixed to supply rails.

Wireless Components

3-6

Specification, August 1999

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