GB1168873A - Low Level D.C. Amplifier - Google Patents

Abstract

1,168,873. Chopper amplifiers. DYNAMCO Ltd. 30 April, 1968 [10 May, 1967], No. 21627/67. Heading H3T. A D.C. amplifier includes input networks R 1 , R 2 , Fig. 5, dividing an input signal at A between two (or more) channels each including an A.C. amplifier A 1 , A 2 , and choppers B, D and C, E which render the amplifiers A 1 , A 2 alternately conducting, one being D.C. restored while the other is conducting, and the outputs being combined at F. The choppers may be electromechanical but preferably they are transistors, B and C being IGFET's, and D and E being NPN transistors. The pair B, D is controlled by a square wave in antiphase to a square wave controlling the pair C, E. R 8 , R 9 are protection resistors. The two choppers associated with each amplifier A 1 , A 2 instead of being connected shunt-wise, may be connected serially in the signal path. In an amplifier arrangement (Fig. 6A, not shown), in which the amplifier of Fig. 5 drives a D.C. amplifier (20), the gain (27, Fig. 6B, not shown) from the input (K) to the amplifiers A 1 , A 2 to the output of the arrangement (20) is selected to be low at lower frequencies relatively to the overall gain (25) of the whole arrangement, measured from the input A, in order to reduce noise arising in the input stages to the amplifiers A 1 , A 2