Detection of amplifier failure

Abstract: In a receiver comprising a receiver filter (12) with a frequency attenuation band and a pilot oscillator (25) for generating a pilot oscillation signal with a pilot frequency in the frequency attenuation band, a coupler (26) couples the pilot oscillation signal and a filtered receiver signal of the receiver filter into a coupled signal. A low noise amplifier (13) amplifies the coupled signal into an amplified signal which comprises an amplified receiver signal derived from the filtered receiver signal and an amplified pilot oscillation signal derived from the pilot oscillation siganl. A branching filter (27) branches the amplified signal into the amplified receiver signal and the amplified pilot oscillation signal. A pilot signal detector unit (28) detects the amplified pilot oscillation signal to produce a direct pilot signal. A failure monitoring unit (29) monitors the direct pilot signal to produce a fault signal when the direct pilot signal is found faulty.

Description: This invention relates to the reliable detection of failure in an amplifier, particularly (but not exclusively) a receiver amplifier for example of the low-noise type. A conventional receiver amplifier comprises an antenna, a receiver filter, a low noise amplifier, and a comparator. The receiver filter is supplied with an input receiver signal from the antenna and filters the input receiver signal into a filtered receiver signal. The low noise amplifier comprises a plurality of amplifier elements. Naturally, electric power is consumed in the low noise amplifier. Therefore, a consumption current is indispensable in the low noise amplifier. The low noise amplifier is supplied with the filtered receiver signal from the receiver filter and amplifies the filtered receiver signal into an amplified signal. The comparator is supplied with a reference signal of a reference level and the consumption current of a consumption level. The comparator compares the consumption level with the reference level to produce a fault signal when the consumption level is lower than the reference level. As will later be described more in detail, the conventional receiver is incapable of reliably detecting a failure in the low noise amplifier. US-A-3.668.533 discloses a control system for maintaining an amplifier operating at a predetermined point in a saturation region of its characteristic. The control system comprises a modulation generator which impresses a small sinusoidal signal in the form of a small amplitude modulation on the carrier wave signal. The signal is applied to a carrier amplifier. A coupler and detector are arranged to sense the magnitude of the output from the carrier amplifier and the detected signal is amplified in an logarithmic amplifier. The output of the logarithmic amplifier is supplied to a phase sensitive detector which is controlled by the modulation generator. An output from the detector is fed to an integrating amplifier, and an output therefrom is used to operate a control element which controls the input power of the signal supplied via the amplitude modulator to the carrier amplifier. JP-A-61167233 describes a self-diagnosing circuit of a two-way CATV relay amplifier. A pilot generator generates a pilot signal having a frequency outside the radio frequency attenuation band and inserts it in the input of an incoming signal low pass amplifier. Its output is branched, detected and compared with a reference level for level check. When the difference between the pilot level and the reference level is a prescribed level or over, an error detection signal is inputted to a state supervisory signal transmitter. SUMMARY OF THE INVENTION It is therefore an object of this invention to provide a receiver which can reliably detect a failure in the low noise amplifier. Other objects of this invention will become clear as the description proceeds. Accordingly, the present invention provides a receiver comprising: a receiver filter having a receiver frequency pass band and a receiver frequency attenuation band for filtering an input receiver signal into a filtered receiver signal; a pilot oscillator for generating a pilot oscillation signal having a pilot frequency in said receiver frequency attenuation band; a coupler connected to said receiver filter and said pilot oscillator for coupling said pilot oscillation signal to said filtered receiver signal to form a coupled signal; a low noise amplifier connected to said coupler for amplifying said coupled signal into an amplified signal which comprises an amplified receiver signal derived from said filtered receiver signal and an amplified pilot oscillation signal derived from said pilot oscillation signal; a branching filter, connected to said low noise amplifier for branching said amplified signal into said amplified receiver signal and said amplified pilot oscillation signal; a receiver terminal connected to said branching filter for receiving said amplified receiver signal; pilot signal detector means connected to said branching filter for detecting only said amplified pilot oscillation signal to produce a direct pilot signal having a pilot signal level; and failure monitoring means connected to said pilot signal detector means for monitoring said direct pilot signal to produce a fault when said direct pilot signal is found faulty; wherein said failure monitoring means comprises: a reference signal producing circuit for producing a reference voltage having a reference level; and a comparator connected to said pilot signal detector means and said reference signal producing circuit for comparing said pilot signal level with said reference level to produce said fault signal when said pilot signal level is lower than said reference level; and said pilot signal detector means comprises: an attenuator connected to said branching filter for attenuating said amplified pilot oscillation signal into an attenuated pilot oscillation signal; and a pilot signal detector connected to said attenuator for detecting said attenuated pilot oscillation signal to produce said direct pilot signal. Brief Description of the Drawing: Fig. 1 is a block diagram of a conventional receiver; Fig. 2 is a block diagram of a low noise amplifier for use in the conventional receiver illustrated in Fig. 1; and Fig. 3 is a block diagram of a receiver according to an embodiment of this invention. Description of the Preferred Embodiment: Referring to Fig. 1, a conventional receiver will first be described for a better understanding of this invention. A receiver filter 12 is connected to the antenna 11 and has a receiver frequency pass band and a receiver frequency attenuation band. The receiver filter 12 is supplied with the input receiver signal from the antenna 11 and filters the input receiver signal into a filtered receiver signal. A low noise amplifier 13 is connected to the receiver filter 12. The low noise amplifier 13 is supplied with the filtered receiver signal from the receiver filter 12 and amplifies the filtered receiver signal into an amplified signal. A receiver terminal 14 is connected to the receiver amplifier 13 and is supplied with the amplified signal from the low noise amplifier 13. Through the receiver terminal 14, the amplified signal is available. A power supply terminal 15 is connected to the low noise amplifier 13 through a current detection resistor 16. A detector current Id flows from the power supply terminal 15 to the low noise amplifier 13 through the current detection resistor 16. A first node 17 between the low noise amplifier 13 and the current detection resistor 16 is connected to a comparator 18. A second node 19 between the power supply terminal 15 and the current detection resistor 16 is connected to the comparator 18. A reference power supply 20 is connected to the comparator 18 and supplies a reference signal having a reference level to the comparator 18. The detector current Id gives a detector voltage of a detector level between the first and the second nodes 17 and 19. The comparator 18 is supplied with the detector voltage and the reference signal. The comparator 18 compares the detector level of the detector voltage with the reference level of the reference signal to produce a fault signal to a fault output terminal 20' when the detector level is lower than the reference level. Turning to Fig. 2, the low noise amplifier 13 comprises first through fourth amplifier elements 21, 22, 23, and 24. The first through fourth amplifier elements 21 to 24 are serially connected to one another. The first amplifier element 21 is connected to the receiver filter 12 and is supplied with the filtered receiver signal from the receiver filter 12. The fourth amplifier element 24 is connected to the receiver terminal 14 and supplies the amplified signal to the receiver terminal. The first amplifier element 21 amplifies the filtered receiver signal into a first amplified signal. The second amplifier element 22 is supplied with the first amplified signal and amplifies the first amplified signal into a second amplified signal. The third amplifier element 23 is supplied with the second amplified signal from the second amplifier element and amplifies the second amplified signal into a third amplified signal. The fourth amplifier element 24 is supplied with the third amplified signal from the third amplifier element 23 and amplifies the third amplified signal into the amplified signal. The first through the fourth amplifier elements 21 to 24 consume first through fourth consumption currents i1, i2, i3, and i4, respectively. The low noise amplifier 13 has a total consumption current Ic which is equal to a sum of the first through the fourth consumption currents i1 to i4. The second consumption current i2 is larger than the first consumption current i1. The third consumption current i3 is larger than the second consumption current i2. The fourth consumption current i4 is larger than the third consumption current i3. The total consumption current Ic is equal to the detector current Id. Each of the first through the fourth consumption currents i1 to i4 becomes smaller when a failure occurs in each of the first through the fourth amplifier elements 21 through 24. Inasmuch as a change of each of the first and the second consumption currents i1 and i2 is extremely smaller than the detector current Id when the failure occurs in each of the first and the second amplifier elements 21 and 22, the detector level is not always lower than the reference level in this event. Consequently, the conventional receiver is incapable of reliably detecting a failure in the low noise amplifier 13. When the total consumption current Ic does not change even if the failure occurs in the low noise amplifier 13, the conventional receiver is incapable of detecting the failure in the low noise amplifier 13. When a failure occurs in a transfer line between the low noise amplifier 13 and the receiver terminal 14, the conventional receiver is incapable of detecting the failure in the transfer line because the failure in the transfer line is not related to the detector current Id. When the total consumption current Ic changes in normal operation of the low noise amplifier 13, the conventional receiver is incapable of reliably detecting the failure in the low noise amplifier 13. This is because the conventional receiver detects in error the failure in the low noise amplifier 13 even when the total consumption current Ic becomes smaller than a reference current in the normal operation of the low noise amplifier 13. Referring to Fig. 3, the description will proceed to a receiver according to a preferred embodiment of this invention. Similar parts are designated by like reference numerals. In Fig. 3, the receiver comprises the antenna 11, the receiver filter 12, a pilot oscillator 25, a coupler 26, the low noise amplifier 13, a branching filter.27, a pilot signal detector unit 28, and a failure monitoring unit 29. The pilot oscillator 25 generates a pilot oscillation signal having a pilot frequency in the receiver frequency attenuation band. The coupler 26 is connected to the receiver filter 12 and the pilot oscillator 25 and is supplied with the filtered receiver signal and the pilot oscillation signal. The coupler 26 couples the pilot oscillation signal and the filtered receiver signal into a coupled signal. Inasmuch as the pilot oscillation signal has the pilot frequency in the receiver frequency attenuation band, the pilot oscillation signal is substantially totally reflected by the receiver filter 12. The pilot oscillator 25 and the low noise amplifier 13 are connected to the power supply terminal 15. The low noise amplifier 13 is connected to the coupler 26 and is supplied with the coupled signal. The low noise amplifier 13 comprises a plurality of amplifier elements in the manner illustrated with reference to Fig. 2. The low noise amplifier 13 amplifies the coupled signal into an amplified signal which comprises an amplified receiver signal derived from the filtered receiver signal and an amplified pilot oscillation signal derived from the pilot oscillation signal. The branching filter 27 is connected to the low noise amplifier 13 and is supplied with the amplified signal. The branching filter 27 branches the amplified signal into the amplified receiver signal and the amplified pilot oscillation signal. The receiver terminal 14 is connected to the branching filter 27 and is supplied with the amplified receiver signal. The pilot signal detector unit 28 is connected to the branching filter 27 and is supplied with the amplified pilot oscillation signal. The pilot signal detector unit 28 comprises an attenuator 30 and a pilot signal detector 31. The attenuator 30 is connected to the branching filter 27 and is supplied with the amplified pilot oscillation signal. The attenuator 30 attenuates the amplified pilot oscillation signal into an attenuated pilot oscillation signal. The pilot signal detector 31 is connected to the attenuator 30 and is supplied with the attenuated pilot oscillation signal. The pilot signal detector 30 detects the attenuated pilot oscillation signal to produce a direct pilot signal having a pilot signal level. The failure monitoring unit 29 is connected to the pilot signal detector 31 and is supplied with the direct pilot signal. The failure monitoring unit 29 comprises the comparator 18 and the reference power supply 20. The comparator 18 is connected to the pilot signal detector 31 and is supplied with the direct pilot signal. The reference power supply 20 produces the reference voltage having the reference level. The comparator 29 is connected to the reference power supply 20 and is supplied with the reference voltage. The comparator 18 compares the pilot signal level with the reference level to produce the fault signal when the pilot signal level is lower than the reference level. The fault output terminal 20' is connected to the comparator 18 and is supplied with the fault signal. While this invention has thus far been described in conjunction with a single embodiment thereof, it will readily be possible for those skilled in the art to put this invention into practice in various other manners. For example, the attenuator 30 may be a variable attenuator capable of changing an attenuation value in response to the reference level.

Claims: A receiver comprising: a receiver filter (12) having a receiver frequency pass band and a receiver frequency attenuation band for filtering an input receiver signal into a filtered receiver signal; a pilot oscillator (25) for generating a pilot oscillation signal having a pilot frequency in said receiver frequency attenuation band; a coupler (26) connected to said receiver filter and said pilot oscillator for coupling said pilot oscillation signal to said filtered receiver signal to form a coupled signal; a low noise amplifier (13) connected to said coupler for amplifying said coupled signal into an amplified signal which comprises an amplified receiver signal derived from said filtered receiver signal and an amplified pilot oscillation signal derived from said pilot oscillation signal; a branching filter, (27) connected to said low noise amplifier for branching said amplified signal into said amplified receiver signal and said amplified pilot oscillation signal; a receiver terminal (14) connected to said branching filter for receiving said amplified receiver signal; pilot signal detector means (28) connected to said branching filter for detecting only said amplified pilot oscillation signal to produce a direct pilot signal having a pilot signal level; and failure monitoring means (29) connected to said pilot signal detector means for monitoring said direct pilot signal to produce a fault when said direct pilot signal is found faulty; wherein said failure monitoring means comprises: a reference signal producing circuit (20) for producing a reference voltage having a reference level; and a comparator (18) connected to said pilot signal detector means and said reference signal producing circuit for comparing said pilot signal level with said reference level to produce said fault signal when said pilot signal level is lower than said reference level; and said pilot signal detector means comprises: an attenuator (30) connected to said branching filter for attenuating said amplified pilot oscillation signal into an attenuated pilot oscillation signal; and a pilot signal detector (31) connected to said attenuator for detecting said attenuated pilot oscillation signal to produce said direct pilot signal. A receiver as claimed in Claim 1, wherein said attenuator (30) is a variable attenuator capable of changing attenuation value.

Inventors: MAKOTO MAETA, NARAHASHI SHOICHI, NOJIMA TOSHIO, OHARA SATORU, SAKAMOTO HIRONORI, MAKOTO, MAETA, NARAHASHI, SHOICHI, NOJIMA, TOSHIO, OHARA, SATORU, SAKAMOTO, HIRONORI
Applicants: JAPAN RADIO CO LTD, NIPPON TELEGRAPH & TELEPHONE, NTT DOCOMO INC, JAPAN RADIO CO., LTD, NIPPON TELEGRAPH AND TELEPHONE CORPORATION, NTT DOCOMO, INC.
Application year: 1992
Main classification: H04B1
IPC codes: H04B17, H04B1