Field deflection circuit for use in a picture display device

Claim 1

A field deflection circuit for use in a picture display device, comprising: an amplifier having an input terminal for receiving a sawtooth-shaped signal of the field frequency, and an output terminal for applying a sawtooth-shaped deflection current having a trace and a retrace to a series network of a field deflection coil; a separating capacitor and a negative feedback resistor coupled to the said output terminal; means for feeding back the voltage across the negative feedback resistor to the amplifier; and a parallel circuit in parallel with said separating capacitor for setting the d.c. component of the voltage across the capacitor at a substantially constant maximum value of a parabolic voltage present across the capacitor during the trace period, wherein the parallel circuit is a clamping circuit comprising a switch which conducts in the first half of the trace period, the conducting interval of the switch ending substantially at the central instant of the trace period, and wherein said switch has a relatively low impedance value during the first half of the trace period, and a relatively high impedance value during the second half of the trace period and during the retrace period.