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TDA8040T

Quadrature demodulator

Philips Electronics 

Philips Semiconductors

Quadrature demodulator

Objective specification

TDA8040T

PINNING

SYMBOL

VCC(A)

I

GND(D)

RF A

RF B

VCC(D)

Q

GND(A)

Qin

Qout

GND(V)

VCOA

VCOB

VCC(V)

Iout

Iin

PIN

DESCRIPTION

1 supply voltage for I and Q amplifiers

2 I channel buffer output

3 demodulator ground

4 RF input A

5 RF input B

6 supply voltage for demodulator

7 Q channel buffer output

8 I and Q amplifiers ground

9 Q channel amplifier input

10 Q channel amplifier output

11 VCO ground

12 VCO tank circuit A

13 VCO tank circuit B

14 supply voltage for VCO

15 I channel amplifier output

16 I channel amplifier input

handbook, halfpage

VCC(A) 1

16 Iin

I2

15 Iout

GND(D) 3

14 VCC(V)

RF A 4

13 VCOB

TDA8040T

RF B 5

12 VCOA

VCC(D) 6

Q7

GND(A) 8

11 GND(V)

10 Qout

9 Qin

MGE510

Fig.2 Pin configuration.

FUNCTIONAL DESCRIPTION

The QPSK modulated RF signal is applied at the input of a

high gain RF amplifier. The amplified signal is then mixed

in a pair of mixers with two LO signals, which are

90 degrees out of phase, to produce the in-phase (I) and

quadrature (Q) signals. These two signals are separately

buffered to drive the external low-pass filters used for the

baseband filtering. The I and Q signals are then amplified

by two matched amplifiers designed to avoid crosstalk

between channels.

The VCO operates at twice the carrier frequency. Its output

signal is applied to a frequency divider (divide-by-2) to

produce the two LO signals which are 90 degrees out of

phase. The VCO is powered from the internal voltage

stabilizer to ensure good shift performance.

1996 Oct 08

4

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