GB1047702A - Parametric amplifiers - Google Patents

Abstract

1,047,702. Parametric amplifiers. K. SCHMID. May 15, 1963 [May 15, 1962], No. 19314/63. Heading H3B. In a parametric amplifier pump energy is stored in a parallel resonant circuit including a centre-tapped inductance forming a bridge with two non-linear capacitors and is phase moduiated by the signal to be amplified, the resultant modulated signal being fed to a phase-sensitive detector having a single-ended output. As shown in Fig. 1, pump power P 1 is supplied to a parallel resonant circuit comprising divided inductance L 1 and two variable capacitance diodes D 1 , D 2 which circuit is tuned to the pump frequency fp and is arranged as a balanced bridge. The signal to be amplified is applied to input 1 so as to cause the average junction capacitances of the pumped diodes to vary with time with the result that the pump energy is amplitude and phase modulated at the signal frequency. The phase modulated signal is then fed to a phase sensitive circuit comprising two detector diodes D 3 , D 4 connected to the parallel resonant circuit and which add the phase modulated pump energy P<SP>1</SP> 1 and the quadrature pump energy P<SP>1</SP> 2 supplied through capacitors C 1 and C 2 . The rectified currents, i.e. the sum and difference of half the pump voltage U 1 appearing across the pump circuit and the voltage at 4 and 6, flows through diodes D 3 , D 4 and resistors R 1 , R 2 to load R L . Thus a phase shift of the pump voltage U 1 alters the magnitude of the voltages applied to detector diodes D 3 , D 4 causing a change in the rectified voltages + UD 3 and - U D4 and hence a change in the output voltage. In a second embodiment, Fig. 2, resistors R 1 , R 2 are connected to ground instead of the tap on inductance L 1 and the polarity of the diode pairs D 1 , D 2 and D 3 , D 4 is chosen such that the output voltage at 7 is in phase with the input voltage 1. The total output voltage is fed back into the input circuit and is in series with the input voltage so that the circuit operates in the manner of a cathode follower. The D.C. component of the output voltage also acts to automatically control the frequency against changes due to the variations of capacitance in the parallel resonant circuit. In the arrangement of Fig. 3 (not shown) the quadrature pump signal P 2 and the pump signal P 1 applied to the bridge circuit are obtained from a signal generator and delay line. For V.H.F. operation as shown in Fig. 3 the pump generator is coupled inductively to the pump circuit but in the case of a low frequency amplifier the tapped inductance may be bifilar wound, Fig. 4 (not shown), allowing coupling of pump signal P 1 by means of a resistor to one end of the tapped inductance. For low frequencies a phase shift network is employed in place of the delay line.