TDA6131 Datasheet, PDF (11/20 Pages) Infineon Technologies AG – Mixer/Oscillator

TDA 6131
preliminary
Functional Description
3.4 Circuit Description
3.4.1 MIXER
The mixer used in this design is a general purpose up-/down conversion gilbert
cell mixer that can be used in various configurations.The RF can enter the IC
either via the pins MIE/MIEX or via MIB/MIBX. Using an external supplied local
oscillator at IN/INX a converted output signal is created at the open collector
output pins MO/MOX. In a second configuration the RF should be connected to
the pins IN/INX and the pins MIB/MIBX/MIE/MIEX need to be connected to an
external tank circuit, thus forming for example an colpitts oscillator using the
internal transistor stages. In both cases the open collector pins MO/MOX need
to be connected to an external supply voltage. To improve the mixer perfor-
mance external resistors at MIE/MIEX make it possible to adjust the mixer cur-
rent. The RF connections to the mixer input can be single ended or balanced,
capacitive or inductive. Supply voltage for the mixer has to be connected to the
pin VCC and to GND.
3.4.2 OSCILLATOR / AMPLIFIER
Using the additional transistor stage it is possible to realize via external compo-
nents an oscillator or an amplifer circuit. Base AB, emitter AE and collector AC
are external available.To adjust the amplifier/oscillator current using a current
mirror the internal reference voltage at VREF has to be connected to BREF with
an external resistor and BREF needs to be connected to the base AB. This can
be done via a resistor and/or a choke. External matching networks at the in- and
output of the transistor stage will improve the amplifier performance.
3.4.3 COMMON
Differential signals and symmetrical circuits are used throughout the mixer part
of the IC.
An internal bias driver generates supply voltage and temperature compensated
reference voltages. The STB pin allows the IC to be switched in a low power
mode. The pins BREF,VREF,STB,VCC,IN,INX,and MO,MOX are ESD pro-
tected.
Wireless Components
3-4
Specification, March 2000