UAA2082 查看數據表（PDF） - Philips Electronics

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UAA2082

Advanced pager receiver

Philips Electronics 

Philips Semiconductors

Advanced pager receiver

Product specification

UAA2082

FUNCTIONAL DESCRIPTION

The complete circuit consists of the following functional

blocks as shown in Figs 1 to 6.

Radio frequency amplifier

The RF amplifier is an emitter-coupled pair driving a

balanced cascode stage, which drives an external

balanced tuned circuit. Its bias current is set by an external

300 Ω resistor R1 to typically 770 µA. With this bias

current the optimum source resistance is 1.3 kΩ at VHF

and 1.0 kΩ at UHF. At 930 MHz a higher bias current is

required to achieve optimum gain. A value of 120 Ω is

used for R1, which corresponds with a bias current of

approximately 1.3 mA and an optimum source resistance

of approximately 600 Ω.The capacitors C1 and C2

transform a 50 Ω source resistance to this optimum value.

The output drives a tuned circuit with capacitive divider

(C7, C8 and C9) to provide maximum power transfer to the

phase-splitting network and the mixers.

Mixers

The double balanced mixers consist of common base

input stages and upper switching stages driven from the

frequency multiplier. The 300 Ω input impedance of each

mixer acts together with external components (C10, C11;

L4, L5 respectively) as phase shifter/power splitter to

provide a differential phase shift of 90 degrees between

the I channel and the Q channel. At 930 MHz all external

phase shifter components are inductive (L10, L11; L4, L5).

Oscillator

The oscillator is based on a transistor in common collector

configuration. It is followed by a cascode stage driving a

tuned circuit which provides the signal for the frequency

multiplier. The oscillator transistor requires an external

bias voltage Vbias(osc) (1.22 V typ.). The oscillator bias

current (typically 250 µA) is determined by the 1.5 kΩ

external resistor R5. The oscillator frequency is controlled

by an external 3rd overtone crystal in parallel resonance

mode. External capacitors between base and emitter

(C17) and from emitter to ground (C16) make the oscillator

transistor appear as having a negative resistance for small

signals; this causes the oscillator to start. Inductance L9

connected in parallel with capacitor C16 to the emitter of

the oscillator transistor prevents oscillation at the

fundamental frequency of the crystal.

The resonant circuit at output pin OSC selects the second

harmonic of the oscillator frequency. In other applications

a different multiplication factor may be chosen.

At 930 MHz an external oscillator circuit is required to

provide sufficient local oscillator signal for the frequency

multiplier.

Frequency multiplier

The frequency multiplier is an emitter-coupled pair driving

an external balanced tuned circuit. Its bias current is set by

external resistor R4 to typically 190 µA (173 MHz), 350 µA

(470 MHz) and 1 mA (930 MHz). The oscillator signal is

internally AC coupled to one input of the emitter-coupled

pair while the other input is internally grounded via a

capacitor. The frequency multiplier output signal between

pins VO1MUL and VO2MUL drives the upper switching

stages of the mixers. The bias voltage on pins VO1MUL

and VO2MUL is set by external resistor R3 to allow

sufficient voltage swing at the mixer outputs. The value of

R3 depends on the operating frequency: 1.5 kΩ

(173 MHz), 820 Ω (470 MHz) and 330 Ω (930 MHz).

Low noise amplifiers, active filters and gyrator filters

The low noise amplifiers ensure that the noise of the

following stages does not affect the overall noise figure.

The following active filters before the gyrator filters reduce

the levels of large signals from adjacent channels. Internal

AC couplings block DC offsets from the gyrator filter

inputs.

The gyrator filters implement the transfer function of a 7th

order elliptic filter. Their cut-off frequencies are determined

by the 47 kΩ external resistor R2 between pins RGYR and

COM. The gyrator filter output signals are available on IF

test pins TPI and TPQ.

Limiters

The gyrator filter output signals are amplified in the limiter

amplifiers to obtain IF signals with removed amplitude

information.

Demodulator

The limiter amplifier output signals are fed to the

demodulator. The demodulator output DO is going LOW or

HIGH depending upon which of the input signals has a

phase lead.

1996 Jan 15

18

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