Method and apparatus for controlling switches.

The present invention relates to a method and apparatus for controlling on/off type switches of the RF part of a radio telephone, without having to draw separate control lines from the logic unit of the telephone to the switches.

The radio part of any modern radio telephone comprises a plurality of controlled switches with which a given electrical circuit can be switched to be active or off, or its parameters can be changed. Said switches are two-position switches, normally bipolar transistors of FETs, and they control, for instance, switchable filters or regulators of the transmitter. Said switches are in turn controlled by the logic unit (processor) of the radio telephone, i.e. a lead, over which a logic "1" or "0", i.e. voltage "high" or "low" is carried to the base of the transistor of FET serving as switch. The logic unit also controls the frequency synthesisers by which the local oscillator frequencies of the transmitter and receiver are produced. As is known in the art, the frequency synthesizer comprises a phase-locked loop (PLL) comprising a phase comparator, a voltage controlled oscillator (VCO), and a programmable divider, dividing the initial frequency of the VCO prior to its being carried to the second input of the phase comparator. The initial frequency of the loop is determined by the above-mentioned programmable divider. The logic unit sets the frequency synthesiser to the desired channel by changing, over a control line, the division numberofthe divider to be consistent with the desired channel. Most usually there are three control lines: by one of said lines the division number is supplied in binary serial form to the register of the phase-locked loop, by a second line a timing signal (clock pulse) is sent, and by the third line, an enable pulse, which on arrival in the phase-locked loop causes the loop-division number supplied to the regi- sterto be transmitted from the registers of the loop circuit to become the contents of the counters.

Also such frequency synthesiser components implemented using one integrated circuit are known in the art in which the control word used for channel change sets certain connecting pins of the circuit to "one" or "zero" state. From said pins, control may be derived for external controlled switches. In said circuits the decoding logic required for implementing the function is integrated into the PLL circuit.

The switch control line methods of prior art are encumbered by some drawbacks. As mentioned above, each controlled switch in the radio unit requires an individual control line from the processor, although in certain instances one control line is able to control a number of switches. Therefore, the more control lines are needed the greater the number of controlled switches in the circuit. This is experienced as an inconvenience when designing a circuit board. If the switches to be controlled and the processor are mounted on separate circuit boards, a multiple pin connector is needed to transfer the control signals from one board to another. If the connecting pins of the PLL circuit are utilised in the control, the number of the pins must be increased, and this leads to larger physical bulk. This is a nuisance in developing telephones of smaller size. Furthermore, it may be noted that PLL components of this type appropriate for portable telephone applications are hard to find.

The present invention discloses a way in which control of switches can be implemented without the above drawbacks.

The present invention provides apparatus for controlling a switch in the radio frequency part of a radio telephone, comprising a logic unit, a frequency synthesiser, at least one control line (a,b,c,) connected to said frequency synthesiser for transmitting control signals from said logic unit to said frequency synthesiser, a switch line (d,e,) for controlling said switch in response to a control voltage supplied by said logic unit, characterised in that said switch line (d,e) is connected to a control line (a,b) such that during the time when said frequency synthesiser is not receiving control signals, the logic unit provides a control voltage over said control line (a,b) and said switch line (d,e) to control said switch.

Preferably, the apparatus includes a low pass filter provided in said switch line (d,e) to inhibit the passage of said control signals to said switch.

In a further preferred embodiment at least two switch lines (d,e) are connected to respective control lines (a,b), no switch line being connected to the control line (c) that transmits the enable pulse from the logic unit.

In another preferred embodiment attenuation resistors are connected to the control lines at their input to the frequency synthesiser to attenuate said control voltage.

The processor of the radio telephone may, during the rest of the time, use the control lines of the PLL circuit as control lines for on/off control of the switches in the RF unit, since the control lines of the phase-locked loop are active only for the time needed in feeding the division number to the registers of the loop circuit, i.e. about millisecond. During that time when the PLL circuit receives no external control, i.e. while no new division number is being supplied, its control lines are in zero state, and the state of the clock and data lines can then be changed without affecting the operation of the PLL circuit in any way. The state of the line by which the enable pulse is supplied must not be changed because it effects a change in the starting frequency of the loop. Therefore, the clock and data lines can indeed be used for controlling the switches. If a plurality of synthesisers are used in the RF unit of the telephone, the control lines of all these are available for controlling the switches.

One embodiment of the invention is described in more detail referring to the accompanying schematic drawing.

Reference numeral 1 refers to a phase-locked loop. A phase-locked loop in its entirety, or parts thereof, most usually the phase comparator and the dividers, are integrated in one chip. The connecting pin K of the circuit receives from the control logic (not shown) timing pulses by the line a, the connecting pin D receives the division number of the loop divider in binary serial form by the line b, and by the line c the enable pulse arrives at the connecting pin E. When the starting frequency of the PLL ciruit is going to be changed, the processor transmits on lines a and b a binary word indicating the clock pulses and the division number. Thereafter, the processor transmits a sharp enable pulse on line c, resulting in the division number within the PLL circuit transferring from the registers to the counter. After the loop has locked onto the selected frequency, the lines a, b and c are in "zero" state. During this time the control voltage for the switches can be transmitted from the processor by the lines a and b, and further by the switch line d connected to the line a, and by the switch line e connected to the line b, to the switches being controlled (not shown), their control thus taking place simply by setting the channel control line and/or clock line of the PLL, as implied by the need of control, to state one or zero. The control voltage can be low frequency compared to the pulses and hence the disturbance caused in the switch lines d and e, by the feeding of division number, is attenuated by means of a low pass filter 2 and 3 included in each line; these filters may be simple RC filters. Hereby, the voltage on lines d and e cannot ascend to such height during the feeding of division numbers that it would cause a change in the state of the switches. The resistors 4 and 5 in the inputs of pins K and D of circuit 1 serve as attenuation resistors. The voltage shapes of the lines are also outlined in the figure.

Using this arrangement, the use of extra switch control lines can be avoided, and it is not necessary to use any such PLL component containing extra logic on the pins of which the control voltage for the switches could be obtained. The lines to the switches can be connected at any point of the control lines. In the connector which may be needed at the interface of the RF part and the logic unit no pins need to be provided for the switch control, hence a smaller connector can be used. The arrangement disclosed hereinabove is simple and inexpensive in implementation.