Patent GB-1271429-A (GB)
Title: Improvements in and relating to electric circuit arrangements
Inventor: ISE YUKIHIKO
IPC: H03H9/54
Filed: 1969-06-26
Abstract: 1,271,429. Duplex signalling. MATSUSHITA ELECTRIC INDUSTRIAL CO. Ltd. 26 June, 1969 [26 June, 1968], No. 32475/69. Heading H4L. [Also in Division H1] A circuit arrangement comprises a piezoelectric device 17, Fig. 1, to which an input at a carrier frequency is applied at terminals 18, 19. The piezo-electric device vibrates resonantly, and gives balanced oppositely phased outputs at the carrier frequency at terminals 20, 21 which are applied to terminals 22, 23 of an impedance network. A composite signal including a suppressed-carrier signal is applied to a third terminal 26 of said network, and balanced components of said composite signal are developed at the terminals 22, 23. These are applied to input terminals 27, 29 of a demodulator 28, from which discrete output signals are given at respective terminals 34, 35. As described, with reference to reception of standard stereophonic sound signals, the output from an FM tuner 10 is applied to a filter 11 to separate out the 19 kc./s. pilot signal. This is applied to a sub-carrier regenerator 12 from which a signal at 38 kc./s. is obtained, which is applied through an amplifier 13 to the input terminal 18 of the piezo-electric device 17, the other input terminal 19 being grounded. The three-terminal network consists of two resistors 24, 25 of equal values, which are connected in series between the terminals 22, 23, and have the terminal 26 at their centre-point. Output from the FM tuner is also applied to a filter 14, which extracts any subsidiary signals, and which passes on the stereo multiplex suppressed-carrier signal to the terminal 26 through an amplifier 15. The demodulator 28 may be of the switching type, arranged as a bridge circuit with input terminals at the ends of one diagonal, and output terminals at the ends of the other, with the arms of the bridge each consisting of a diode and a resistor in series. The outputs of the demodulator, corresponding respectively to the left (L) and right (R) channel signals, are taken to terminals 34, 35 through amplifiers 31, 33. The piezo-electric device 17 is formed as a thin rectangular plate of ceramic material, with pairs of opposed electrodes on its two major surfaces. As shown in Fig. 8, there are three pairs of opposed electrodes 61, 62; 63, 64 and 65, 66 which are parallel to the length of the plate and which are disposed symmetrically with respect to the longitudinal median axis X-X<SP>1</SP> thereof. Terminals 67, 68; 69, 70 and 71, 72 are respectively provided for the electrodes. The electrodes 61, 62; 65, 66 are for the input and the output, respectively, whilst the central electrodes 63, 64 are grounded, and provide electrostatic shielding. Said central electrodes may be omitted (Fig. 7, not shown). In an alternative construction two pairs of opposed electrodes for the input and the output, respectively, are provided which are at 90 degrees to the electrodes 61, 62 and 65, 66 as shown in Fig. 8, and which are disposed symmetrically with respect to the transverse median axis of the plate (Fig. 2, not shown).