ML13176 View Datasheet(PDF) - LANSDALE Semiconductor Inc.

Part Name

Description

Manufacturer

ML13176

UHF FM/AM Transmitter

LANSDALE Semiconductor Inc. 

ML13175/ML13176

LANSDALE Semiconductor, Inc.

Legacy Applications Information

Manufacturers specify crystal for either series or parallel res-

onant operation. The frequency for the parallel mode is cali-

brated with a specified shunt capacitance called a “load

capacitance.” The most common value is 30 to 32 pF. If the

load capacitance is placed in series with the crystal, the

equivalent circuit will be series resonance at the specified

parallel–resonant frequency. Frequencies up to 20 MHz use

parallel resonant crystal operating in the fundamental mode,

while above 20 MHz to about 60 MHz, a series resonant

crystal specified and calibrated for operation in the overtone

mode is used.

APPLICATION EXAMPLES

Two types of crystal oscillator circuits are used in the appli-

cations circuits: 1) fundamental mode common emitter

Colpitts (Figures 1, 17a, 17b and 21) and 2) third overtone

impedance inversion Colpitts (also Figures 1 and 21).

The fundamental mode common emitter Colpitts uses a par-

allel resonant crystal calibrated with a 32 pf load capacitance.

The capacitance values are chosen to provide excellent fre-

quency stability and output power of > 500 mVp–p at Pin 9.

In Figures 1 and 21, the fundamental mode reference oscilla-

tor is fixed tuned relying on the repeatability of the crystal

and passive network to maintain the frequency, while in the

circuit shown in Figure 17, the oscillator frequency can be

adjusted with the variable inductor for the precise operating

frequency.

The third overtone impedance inversion Colpitts uses a series

resonance crystal with a 25 ppm tolerance. In the application

examples (Figures 1 and 21), the reference oscillator operates

with the third overtone crystal at 40.0000 MHz. Thus, the

ML13175 is operated at 320 MHz (fo/8 = crystal; 320/8) =

40.0000 MHz. The resistor across the crystal ensures that the

crystal will operate in the series resonance mode. A tuneable

inductor is used to adjust the oscillation frequency; it forms a

parallel resonant circuit with the series and parallel combina-

tion of the external capacitors forming the divider and feed-

back network and the base–emitter capacitance of the

devices. If the crystal is shorted, the reference oscillator

should free–run at the frequency dictated by the parallel reso-

nant LC network.

The reference oscillator can be operated as high as 60 MHz

with a third overtone crystal. Therefore, it is possible to use

the ML13175 up to at least 480 MHz and the ML13176 up to

950 MHz (based on the maximum capability of the divider

netowork).

ENABLER (Pin 11)

The enabling resistor at Pin 11 is calculated by:

Reg. enable = VCC – 1.0 Vdc/lreg. enable

From Figure 4, lreg.enable is chosen to be 75µA. So, for a

VCC = 3.0 Vdc Rreg.enable = 26.6 kΩ, a standard value 27

kΩ resistor is adequate.

LAYOUT CONSIDERATIONS

Supply (Pin 12): In the PCB layout the VCC trace must be

kept as wide as possible to minimize inductive reactance

along the trace; it is best that VCC (RF ground) completely

fills around the surface mounted components and intercon-

nect traces on the circuit side of the board. This technique is

demonstrated in the evaluation PC board.

BATTERY/SELECTION/LITHIUM TYPES

The device may be operated from a 3.0 V lithium battery.

Selection of a suitable battery is important. Because one of

the major problems for long life battery powered equipment

is oxidation of the battery terminals, a battery mounted in

clip–in socket is not advised. The battery leads or contact

post should be isolated from the air to eliminate oxide

build–up. The battery should have PC board mounting tabs

which can be soldered to the PCB. Consideration should be

given for the peak current capability of the battery. Lithium

batteries have current handling capabilities based on the com-

position of the lithium compound, construction and the bat-

tery size. A 1300 mA/hr rating can be achieved in the cylin-

drical cell battery. The Rayovac CR2/3A lithium–manganese

dioxide battery is a crimp sealed, spiral wound 3.0 Vdc, 1300

mA/hr cylindrical cell with PC board mounting tabs. It is an

excellent choice based on capacity and size (1.358” long by

0.665” in diameter).

DIFFERENTIAL OUTPUT (Pins 13, 14)

The availability of micro–coaxial cable and small baluns in

surface mount and radial–leaded components allows for sim-

ple interface to the output ports. A loop antenna may be

directly connected with bias via RFC or 50 Ω resistors.

Antenna configuration will vary depending on the space

available and the frequency of operation.

AM MODULATION (Pin 16)

Amplitude Shift Key: The ML13175 and ML13176 are

designed to accommodate Amplitude Shift Keying (ASK).

ASK modulation is a form of digital modulation correspon-

ding to AM. The amplitude of the carrier is switched between

two or more values in response to the PCM code. For the

binary case, the usual choice is On–Off Keying (often abbre-

viated OOK). The resultant amplitude modulated waveform

consists of RF pulses called marks, representing binary 1 and

spaces representing binary 0.

Page 12 of 16

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