| 摘要 |
1,065,383. Transistor amplifying circuits. AKUSTISCHE U. KINO-GER€TE G.m.b.H. May 19, 1964 [May 20, 1963], No. 20548/64. Heading H3T. The invention relates to a circuit for a capacitive transducer, being of the modulated high frequency type and comprising an oscillator A which includes the primary winding of a transformer œ 1 , the secondary of which is centretapped and is shunted by the capacitive transducer C 0 in series with a fixed capacitor C 1 . A bridge type detector circuit is formed in conjunction with diodes D 1 , D 2 which are connected to impedance-matching transformer windings S 1 , S 2 respectively, a low frequency output being obtained via audio transformer œ 2 . According to the invention, efficiency is increased and the signal to noise ratio improved by replacing the H.F. choke which, in the known circuit connects the centre-tap of the secondary of the transformer œ 1 with the join of capacitors C 0 , C 1 , by a resonant circuit Lr, Cr or bandpass network. This is tuned to a frequency offset from the frequency of oscillation and gives an increased output by virtue of the frequencymodulation which occurs when the transducer C 0 varies in capacity. |
