High-performance GaAs heterojunction bipolar transistor logarithmic IF amplifier

A DC-4-GHz true logarithmic amplifier: theory and implementation

“…A common implementation consists of two differential pairs in parallel with shared collector nodes, as shown in Fig. 4 [7]- [9]. One differential pair uses emitter degeneration to provide low gain and the other differential pair is undegenerated to provide high gain.…”

“…5 or 6 is just on the point of limiting, then the input is (7) However, is known from (5) to be , so that (8) Additionally, if the path is limiting, then there are paths with higher gains which are also limiting, and more paths which are still amplifying linearly. Thus, the output current is (9) Using (2) and then (4)…”

A Current‐mode Logarithmic Function Circuit

“…This justifies the continuing interest in developing logarithmic function circuits manifested by the relatively large number of publications in this area; see for example Refs. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] and the references cited therein. Traditionally, a logarithmic function circuit, with input voltage and output voltage (or current) can be realized by exploiting to advantage the inherent exponential transconductance characteristic of the pn junction in a diode [12], bipolar transistor [5], or LED [16], to introduce the required nonlinearity into a circuit based on a current-feedback-operational [12], a transimpedance-amplifier [19], an operational-amplifier [1,16], a transconductance-feedback-amplifier [18], or a current-conveyor [13].…”

“…Alternatively, a pseudo-logarithmic function can be implemented using piecewise linear approximations and cascaded limiting amplifiers [6]. This logarithmic function can be realized in GaAs hetrojunction bipolar transistor (HBT) technology [2,3], GaAs MESFET technology [4,15], bipolar, CMOS or BiCMOS technology [8][9][10][11]14]. On the other hand, current mode circuits, with current inputs and current outputs, enjoy the attractive features of a wide current signal dynamic range even with low power supply voltages and wide bandwidths.…”