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LANSDALE Semiconductor, Inc.

ML13146

General

The ML13146 consists of a low power amplifier, a 50

Ω lin-

ear mixer with linearity control, divide by 64/65 dual modulus

prescaler and LPA. This device is designated for use as the low

power transmitter in analog and digital FM systems such as

UHF and 800 MHz Special Mobile Radio (SMR), UHF Family

Radio Services, PCS and 902 to 928MHz cordless telephones.

It features a mixer linearity control to preset or auto program

the mixer dynamic range, an enable function and a wideband

mixer output so the IC may be used either as an up converter

or for a direct conversion source. Additional details are covered

in the Pin by Pin Description which shows the equivalent inter-

nal circuit and external circuit requirements.

Current Regulation/Enable

The device features temperature compensating, voltage inde-

pendent current regulators which are controlled by the enable

function in which “high” powers up the IC.

Mixer: General

The mixer is a double–balanced four quadrant multiplier

biased class AB allowing for programmable linearity control

via an external current source. An input third order intercept

point of 20 dBm has been achieved. The mixer has a 50

Ω sin-

gle–ended RF input and open collector differential outputs. An

onboard Local Oscillator transistor has the emitter, base and

collector pinned out to implement a low phase noise VCO in

various configurations. Additionally, a buffered prescaler out-

put is provided for operation with a low frequency synthesizer.

For direct conversion applications the input of the mixer may

be terminated to ground through a 120 to 330

Ω resistor.

Local Oscillator/Voltage Control Oscillator

The on–chip transistor operates with coaxial transmission

line or LC resonant elements to over 1.8 GHz. Biasing is done

with a temperature/voltage compensated current source in the

emitter. A RFC from VCC to the base is recommended.The

transistor can be operated in the classic Colpitts, Clapp, or

Hartley configuration. The application circuit (Figure 8)

depicts a parallel resonant VCO which can cover the entire 902

to 928 MHz frequency band with phase noise of approximately

–80 dBc/Hz at a 10 kHz offset (see Figure 2). For this configu-

ration, the LO will be driven with approximately 100 mVrms,

and the frequency of oscillation can be approximated by:

where Cv is the equivalent capacitance of the varactor at the

control voltage.

For higher frequency operation, a series tuned oscillator con-

figuration is recommended. Table 1 contains the S–parameters

for the VCO transistor in a common collector configuration.

This information is useful for designing a VCO at other operat-

ing frequencies or for various other oscillator topologies.

The output power (at Mix/Buf Out) can be varied by adjust-

ing the value of R5 as illustrated in Figures 3 and 4. Figure 5

shows the typical operating window for the prescaler.

CIRCUIT DESCRIPTION