AU600861B2

AU600861B2 - Portable radio transmitter

Info

Publication number: AU600861B2
Application number: AU23590/88A
Authority: AU
Inventors: Otto Eigner
Original assignee: Individual
Current assignee: Individual
Priority date: 1987-10-23
Filing date: 1988-10-23
Publication date: 1990-08-23
Anticipated expiration: 2008-10-10
Also published as: AU2359088A

Description

i COMMONWEALTH OF AUSTRI 0 FORM PATENTS ACT 1952 r M P T. T 9PFrTFTrAT TInN FOR OFFICE USE: Class Int.Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority: ~P.Elated Art: "t 4ame of Applicant: Address of Applicant: ctual Inventor: Sctual Inventor: OTTO EIGNER 1,11 Percival Road, Smithfield, New South Wales 2164, Australia Otto Eigner tAddress for Service: SHELSTON WATERS, 55 Clarence Street, Sydney Complete Specification for the Invention entitled: S"PORTABLE RADIO TRANSMITTER" c r C C I The following statement is a full description of this invention, including the best method of performing it known to me:- 1 Complete of PI 5054 dated 23rd October, 1987 4 :i l This invention concerns a portable radio transmitter for transmitting a selected code. Such transmitters have a particular application as personal security devices and as emergency communication devices. The transmitters may have a range of a few hundred meters and be worn by bank staff, service station attendants and the like in order to signal to a centralised alarm system when the person is in any danger. The transmitters cah also be used by elderly or sick persons to summon emergency assistance.

Such transmitters clearly also have applications in the remote control field.

r Transmitters of this type commonly operate in the C r 27Mhz band (usually defined as 26,937 to 27,282Mhz). In c the past such transmitters have comprised a 27Mhz crystal C controlled transistor oscillator followed by a transistor ,ower amplifier coupled to the radio frequency (RF) load in the form of an antenna or a ferite rod. In practice this design requires two circuits: a linear circuit to c r generate the 27Y'hz carrier and effect the necessary amplification; and a digital circuit to encode the fransmitter. The coded carrier is fed to the RF load via cc tuning coils which are necessary to match the RF load to CcCLC the power amplifier stage.

c c According to the invention there is provided a portable radio transmitter for transmitting a selected code, the transmitter including a CMOS integrated circuit gate array which comprises an encoder, a logic gate and a buffer; wherein the logic gate is connected in positive 2

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feedback relationship with an external crystal to generate a radio frequency carrier, the encoder is connected to deviate the crystal frequency, and the buffer is connected between the output of the logic gate and an output terminal; wherein a single capacitor directly interconnects a radio frequency load and the output terminal.

Advantageously the value of the single capacitor is selected to match the output impedance of the buffer to the impedance of the RF load. The radio frequency load may comprise a tuned ferite rod antenna in parallel with a capacitance in which case the value of the single capacitance is selected having regard to the value of that capacitance.

Preferably, the portable radio transmitter transmits a selected code modulated onto a 27Mhz carrier frequency.

The advantages of the invention are that, by using a digital oscillator formed by a crystal in positive feedback arrangement with a logic gate to generate the RF carrier, both the oscillator and power amplifier stages, as well as the encoder and buffer, can be realised in a single CMOS integrated circuit chip; and also that the RF output of the CMOS chip may be connected to the RF load via a capacitor without the need for any intervening coils.

The invention will now be described by way df example only with reference to the accompanying drawing which shows a schematic illustration of a radio transmitter embodying the invention.

.4 3 ~i- I 1 1% i;iy;~t i~ i i Radio transmitter 1 is a self-contained and portable unit having some kind of attachment means whereby the unit can be worn by a user. For instance, by hanging the transmitter around his neck. Transmitter 1 may be battery powered, in which case the battery compartment may be accessed via an opening in order that the batteries may be replaced from time to time as they run down.

Inside transmitter 1 are a CMOS integrated circuit gate array 2, a power supply switch 3, a crystal 4, a radio frequency (RF) load 5 and a capacitor 6.

vote Integrated circuit 2 includes an encoder 7, logic gate 8 S: and buffer 9. Buffer 9 consists of a number of paralleled digital gates, only the last stage of which is shown. A pair of power supply terminals 10, a pair of crystal terminals 11 and an output terminal 12 connect integrated circuit 2 to the other components.

Power supply terminals 10 are connected to the S battery in the battery compartment. One of the terminals 2Q,. 10 being connected via switch 3 which may be closed by any suitable means in order to activate the transmitter.

For example, a button may be provided on the outside of the unit.

One input of gate 8 is connected to one of the crystal terminals 11, and the output of gate 8 is connected to the other crystal terminal. Crystal 4 and logic gate 8 are preferably arranged to provide stable oscillation substantially at 27Mhz. The output of gate 8 4 i o ur~ :rl '7 is connected to buffer 9. The output of buffer 9 is connected to terminal 12.

The output of encoder 7 is connected to terminal 13 and is used to deviate the crystal frequency, via circuitry 14 of substantially known type, according to the selected code.

The RF signal from output 12 is coupled directly to the radio frequency (RF) load via capacitor 6. The RF load comprises a tuned ferite rod antenna 15 in parallel with a capacitance 16.

CMOS integrated circuits are symmetrically switching devices and the final stage of the CMOS buffer circuit 9 comprises a pair of switches synchronously operated in push pull relationship to deliver power to the RF load.

Since the switches are switched symmetrically between j high and low values and the RF load has a narrow band of natural frequencies, the output to the RF load closely approximates an alternating current signal and therefore load-matching is greatly simplified and can be effected using only a coupling capacitor 6. Careful selection of S the value of coupling capacitor 6 relative to the value t 1 of capacitance 16 will achieve optimum impedance coupling S l resulting in a very highly efficient use of battery power. This ensures a long battery life, and/or allows a Ssmaller battery to be used which is of particular benefit in transmitters of this type.

I

Claims

1. A portable radio transmitter for transmitting a selected code, the transmitter including a CMOS integrated circuit gate array which comprises an encoder, a logic gate and a buffer; wherein the logic gate is connected in positive feedback relationship with an external crystal to generate a radio frequency carrier, the encoder is connected to deviate the crystal frequency, and the buffer is connected between the output of the logic gate and an output terminal; and wherein a single capacitor directly interconnects a radio frequency load and the output terminal.

2. A portable radio transmitter as claimed in Claim 1 wherein the value of the single capacitor is selected to r ct l match the output impedance of the buffer to the impedance Tk tr t of the RF load. e r

3. A portable radio transmitter as claimed in Claims 1 or 2 wherein the radio frequency load comprises a tuned ferite rod antenna in parallel with a capacitance.

4. A portable radio transmitter as claimed in any s. preceding claim arranged to transmit a selected code modulated onto a 27Mhz carrier frequency. C e5. A portable radio transmitter substantially as ft• hereinbefore described with reference to the accompanying drawings. DATED this 10th day of October 1988 OTTO EIGNER r, Attorney: PETER HEATHCOTE Fellow Institute of Patent Attorneys of Australia of SHELSTON WATERS 6