3-7

must be taken into consideration when setting the current

source value.

Figure 3B depicts the use of a common resistor sharing the

current through the cell which is used for temperature

Figure 3C uses a split supply.

Design Example: Down Converter Mixer

Figure 4 shows an example of a low cost mixer for cellular

applications.

The design flexibility of the HFA3101 is demonstrated by a

low cost, and low voltage mixer application at the 900MHz

range. The choice of good quality chip components with their

self resonance outside the boundaries of the application are

important. The design has been optimized to accommodate

the evaluation of the same layout for various quiescent

became important for the available overhead and also for

maintaining an AC true impedance for high frequency

signals. The value of 27

Ω has been found to be the optimum

minimum for the application. The input impedances of the

HFA3101 base input ports are high enough to permit their

termination with 50

Ω resistors. Notice the AC termination by

decoupling the bias circuit through good quality capacitors.

The choice of the bias has been related to the available

of the cell quiescent currents, the voltage at the emitter

The gain of the circuit, being a function of the load and the

combined emitter resistances at high frequencies have been

kept to a maximum by the use of an output match network.

The high output impedance of the HFA3101 permits

FIGURE 3A.

FIGURE 3B.

FIGURE 3C.

FIGURE 3.

27

390nH

0.01

0.01

110

220

0.1

3V

75MHz

2K

5p TO 12p

LO IN

51

825MHz

51

900MHz

IF OUT

RF IN

0.01

0.01

0.01

330

FIGURE 4. 3V DOWN CONVERTER APPLICATION

HFA3101