Parallel hybrid type of DC amplifier using modified magnetic modulator

This paper describes the design of a parallel hybrid type of dc amplifier which consists of a modified magnetic modulator and an ac-coupled amplifier. The modified magnetic modulator is very simple and highly accurate, incorporating bifilar windings for both input and output signals without a bandpass filter or selective amplifier. With this design it is possible to connect a high gain, ac amplifier in parallel without saturation because of decreased symmetrical components of the input winding of the modulator. The present dc amplifier can easily achieve high-input resistance and stabilized gain by the customary use of negative feedback. An equivalent of the input noise voltage and current of the parallel hybrid type of dc amplifier of about 5 × 10
⁻⁸
V
pp
/√Hz and 3 × 10
⁻⁹
A
pp
/√Hz at a range from dc to 10 KHz of the bandwidth of the system, and thermal drift of 5 × 10
⁻⁸
V
pp
/°C and a long-term drift of 5 × 10
⁻⁸
V
pp
/day were achieved.