GB2438257A

GB2438257A - Receiving apparatus having a low quiescent current

Info

Publication number: GB2438257A
Application number: GB0610068A
Authority: GB
Inventors: Kevin Trevor Talbot; Jeremy John Greenwood
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2006-05-20
Filing date: 2006-05-20
Publication date: 2007-11-21
Anticipated expiration: 2026-05-20
Also published as: GB2438257B; GB0610068D0

Abstract

Receiving apparatus suitable for use in a vehicle remote locking system uses a switched mode power supply (1) to minimise current drain on the vehicle's battery. To mitigate against the deleterious effects of switching noise on the receiver (2), the receiver and power supply are enabled and disabled in synchronism with the incoming pulsed signal. A reservoir capacitor (3) powers the receiver while the power supply is disabled.

Description

Receiving Apparatus Having a Low Quiescent Current This invention

relates to receiving apparatus having a low quiescent current, such as apparatus having particular application in remote locking devices for motor vehicles.

Remote locking systems typically include a radio frequency (RF) transmitter contained within a hand-held device (e.g. key fob) and a vehicle-mounted receiver. The signals transmitted typically comprise a sequence of RF data pulses.

The sequence usually comprises a preamble followed by an ID code which is specific to the vehicle.

While the transmitter is activated only when a button on the key fob is pressed, the receiver needs to be constantly powered up, on standby, ready to receive the ID-coded signal.

This is a constant drain on the vehicle's battery.

In fact, vehicle-mounted receivers are one of the biggest consumers of quiescent current from the vehicle's battery.

As the operating voltage of a typical receiver is less than volts, most of the power consumed from the vehicle's (12V) battery ends up as heat dissipated in the linear regulator.

One way of reducing quiescent current, and having a general application, is to use a switched-mode power supply.

However, the radio frequency emissions generated by the switching process tend to raise the background noise levels and, consequently, de-sensitise the receiver.

Hence it would be advantageous to provide a receiving apparatus having a low quiescent current and being less susceptible to power switching noise.

According to the present invention there is provided receiving apparatus comprising; a receiver for receiving a signal comprising a sequence of RF pulses having a known format and transmitted from a remote transmitter, a power supply for supplying electrical power to the receiver and including a switched-mode power unit and a reservoir capacitor, and a control module, connected to the receiver, for generating a blanking signal for periodically enabling and disabling the switched-mode power unit and wherein the periods during which the switched-mode power unit is disabled coincide with periods of RF pulse transmission.

The invention enables a switched-mode power supply to be used in combination with a blanking signal which can switch the switched-mode power supply on for periods coincident with silent periods in transmission i.e. whenever an RF pulse ends there is always a certain minimum time before the next pulse.

So noise generated during the switching operation does not interfere with the reception of RF pulses.

The reservoir capacitor maintains electrical power to the receiver while the switched-mode power unit is disabled.

During periods where the switched-mode power unit is enabled, it will charge up the capacitor.

In a preferred embodiment, the blanking signal is also used to enable and disable the receiver such that the receiver is enabled to detect the transmitted signal during periods when the switched-mode power unit is disabled, and the receiver is disabled while the switched-mode power unit is enabled, and wherein the periods during which the receiver is enabled are synchronised with the transmitted signal such that at least a portion of each RF pulse comprising said signal is detected by the receiver.

For example, in the case of a simple AM (amplitude modulation) receiver, the blanking signal can be used to freeze the data slicer of the receiver while the power supply is enabled.

Once a preamble comprising the transmission has been detected by the receiver, the control module can synchronise the blanking signal so that at least a portion of each subsequent pulse can be detected and then demodulated.

Some embodiments of the invention will now be described, by way of example only, with reference to the drawings of which; Fig. 1 is a schematic block diagram of receiving apparatus in accordance with an embodiment of the invention, Fig. 2 is a diagram of waveforms illustrating a first mode of operation of the embodiment of Fig. 1, and Fig. 3 is a diagram of waveforms illustrating the operation of an alternative mode of operation.

With reference to Fig. 1, receiving apparatus comprises a switched-mode power unit 1 which supplies electrical power to a receiver 2 and charging current to a reservoir capacitor 3.

A control module 4 has an input which is connected to an output of the receiver 2. The control module 4 also has an output which is connected to both the receiver 2 and the power unit 1.

The apparatus of Fig. 1 is suitable for use as part of a remote locking/unlocking security system for a motor vehicle in which case, the power unit 1 is connected up to receive a current supply from the vehicle's battery (not shown) on line 5. Further, the receiver 2 is configured to receive radio signals from a remote transmitter via an antenna 6.

The radio signals comprise a message, typically a sequence of RF data pulses. The length of the message, the frequency of the RF carrier and the data rate are known to the receiver 2 and control module 4. The receiver is configured (in a conventional manner) to demodulate and decode the message to provide a data outpuL on line 7 for further use, as appropriate, by a vehicle security control system (not shown).

A first mode of operation will now be described with reference to Fig. 2.

Waveform A represents the first few RF data pulses of an incoming message, commencing at time to and having a data rate of 1/T.

Waveform B is a blanking signal generated by the control module 4 and fed into the receiver 2 and power unit 1.

The blanking signal alternates between high and low states at a rate comparable with the data rate 1/T. When the blanking signal is low, the receiver 2 is enabled and the power unit 1 is disabled. During these periods the receiver 2 is powered by the reservoir capacitor 3. When the blanking signal is high, the receiver is disabled and the power unit is enabled. During these periods, the power unit 1 charges up the reservoir capacitor 3. The period for which the blanking signal is low (receiver on) is longer than the period for which it is high (receiver off).

Waveform C represents the high frequency noise signals generated as the power unit 1 switches on and off.

Waveform D represents the output signal of an analogue stage of the receiver 2 which is fed into the control module 4.

Between t1 and t2, the receiver 2 detects a portion of two incoming RF pulses, at least one of the portions being of sufficient duration for the control module 4 to commence synchronisation of the blanking signal (waveform B) with the incoming data pulse stream (waveform A). Hence the blanking signal is re-adjusted at t3 so that, all the subsequent transmitted pulses can be clearly received without interference from switching noise.

In an alternative mode of operation, the blanking signal is used only to switch the power unit 1. The receiver 2 is enabled all the time. Also in this embodiment, the power unit is disabled for the entire length of the message and the receiver 2 is powered solely by the capacitor during this period.

With reference to Fig. 3, waveform E represents the message comprising four pulses which commences at time t1 and ends at time t2 Waveform F is the blanking signal used to switch the power unit 1. When the blanking signal is high the power unit is enabled. When the blanking signal is low, the power unit is disabled.

Waveform G represents power supply switching noise signals.

Waveform H represents the output signal from the analogue stage of the receiver 2 which is fed into the control module 4.

Prior to time t, the blanking signal alternates between high and low states as in the first example described with reference to Fig. 2.

Between to and t1 the receiver detects the first pulse although part of it could be masked by switching noise. On detection of the pulse, the control module 4 knows that a message is coming in and maintains the power unit 1 in a disabled state until the end of the message at t2 whereupon, the blanking signal resumes its initial periodic form.

During reception of the message between t1 and t2 there is no switching noise to cause any interference in the receiver.

Claims

CLA I MS

1. Receiving apparatus comprising; a receiver for receiving a signal comprising a sequence of RF pulses having a known format and transmitted from a remote transmitter, a power supply for supplying electrical power to the receiver and including a switched-mode power unit and a reservoir capacitor, and a control module, connected to the receiver,-for generating a blanking signal for periodically enabling and disabling the switched-mode power unit and wherein the periods during which the switched-mode power unit is disabled coincide with periods of RF pulse transmission.

2. Receiving apparatus according to claim 1, wherein the blanking signal is also used to enable and disable the receiver such that the receiver is enabled to detect the transmitted signal during periods when the switched-mode power unit is disabled, and the receiver is disabled while the switched-mode power unit is enabled, and wherein the periods during which the receiver is enabled are synchronised with the transmitted signal such that at least a portion of each RF pulse comprising said signal is detected by the receiver.

3. Receiving apparatus substantially as hereinbefore described with reference to the drawings.