Chapter 12 "Discrete OP-Amp Ⅱ"

voltage feedback type discrete OP-Amp【学習編】

　Trで差動増幅回路を組む場合、そのバイアス電流と入力抵抗について考慮する必要があり、それらによって生じる(+)入力端子電圧と(－)入力端子電圧を揃える様にしなければ、出力にgain倍されたオフセット電圧が発生します。そこで、オフセット電圧を抑える為の回路構成を学習して行きたいと思います。

(Complementary Differential input pairs)

...There are many performance advantage to a well-design mirror-image topology. Since both differential input stage are working in opposing directions to each other, various undesirable offset traits are effectively nulled out. The input stage of Fig 4.10(a) measured a 12-mV DC offset at the input --- still not perfect but a severalfold improvement over the circuit in Fig 4.8(a). However, the DC offset at the output of the VA stage lowered to a fantastic 156-uV offset! Admittedly, some of this improvement is also a contribution of the push-pull VA stage, but a push-pull VA stage cannot be utilized with the circuit of Fig 4.8(a),so the issue becomes irrelevant.
  A mirror-image topology exhibits a very desirable type of mode rejection in two separate planes simultaneously. For example, if we can think of a single differential amplifier stage as rejecting a common mode signal in the horizontal plane (i.e., a common signal on each input ---the line drown from input to input being a horizontal line), we can describe a mirror-image topology as rejecting "differential" signals on the "vertical" plane. In other words, various types of differences (that is, Vbe mismatches, resistor tolerances, small DC offsets, etc.) will have the tendency to be nulled or greatly reduced in their effect. ... 

以下、各々の実例を調べてみたいと思います。