TRF5901

SINGLE-CHIP RF TRANSCEIVER

SWRS014 – DECEMBER 2002

11

POST OFFICE BOX 655303

RF mixer

The RF mixer is designed to operate with the on-chip VCO. If an external LO is used, a typical drive level of

–10 dBm should be applied at the VCO input terminal. The mixer is a conventional double-balanced Gilbert cell

mixer designed to provide a high IP3, typically 1 dBm.

Since the mixer output’s push-pull amplifier has a 330-

Ω output impedance, a conventional 330-Ω ceramic filter

can be directly connected to the output without additional matching. The mixer output can also be directly

connected to the second IF amplifier/limiter input terminal, IF2_IN, through a single conventional 330-

Ω ceramic

filter, thus bypassing the first IF amplifier.

Figure 5 and Figure 6 show the RF mixer input and output impedances, respectively.

Figure 5. Typical RF Mixer Input Impedance

(S11) at Device Terminal MIX_IN

Figure 6. Typical RF Mixer Output Impedance

(S22) at Device Terminal MIX_OUT

0.5

1

↑1 U

2

5

10

2

1

0.5

0.2

0

–0.5

–1

–2

–5

START 850 MHz

STOP 950 MHz

CH1 S11

CAL

OFS

CPL

FIL

1k

↑1 U

START 5 MHz

STOP 25 MHz

CH1 S22

CAL

OFS

CPL

FIL

1k

1

5

0.5

1

2

5

10

2

1

0.5

0.2

0

–0.5

–1

–2

–5

5

1

first IF amplifier

The first IF amplifier provides a typical gain of 7 dB to compensate for losses caused by a ceramic filter. The

input and output of the first IF amplifier is matched internally to 330

Ω, permitting direct connections to 330-Ω

ceramic filters. If filters with different impedances are used, an impedance matching network is required.

A second filter can be connected between the first IF amplifier and the second IF amplifier/limiter to increase

the receiver selectivity. Alternately, the RF mixer output can be directly connected to the second IF amplifier as

shown in Figure 7. A single ceramic filter can also be used to connect terminal 41 to terminal 39. In this case,

a 0.1-

µF dc-blocking capacitor should be used to connect terminal 44 to 42 to maximize receiver sensitivity.