Abstract
This study proposes a capacitive feedback transimpedance amplifier (CF-TIA) using a transistor in the direct current (DC) feedback loop for high DC dynamic range. In some applications, the background DC input can vary widely from the minimum to the maximum, and TIA have to sense the target signal even on the top of the maximum DC input. In a conventional CF-TIA, however, the allowable DC input is constrained by the value of the resistor in the DC feedback loop. To allow a fairly high DC input, the resistor is set to a very low value. This causes the thermal noise current to increase significantly. The increased thermal noise is always present even in the minimum DC input, thus degrading the overall noise performance. The circuit proposed herein overcomes this shortcoming by using the transistor instead of the resistor. The adverse effect of the parasitic capacitance of the transistor on system stability is compensated for as well. Then, the analyses of the overall frequency response and design parameters, including the cut-off frequency and attenuation ratio associated with system stability, are presented for the proposed circuit. In addition, in order to cope with the problem that stability is dependent on the amount of DC input, a simple method for ensuring system stability regardless of DC component value is introduced. The presented analyses and the method are generalized for all CF-TIA applications.
Highlights
This study proposes a capacitive feedback transimpedance amplifier (CF-TIA) using a transistor in the direct current (DC) feedback loop for high DC dynamic range
Our system avoids the shortcoming of the conventional CF-TIA, whereby the thermal noise for the maximum DC input always present even in normal or low DC
The thermal noise is replaced by the shot noise varying with DC
Summary
Precision instrumentation systems, such as optical receivers [1], electrical sensors [2,3,4,5], emerging biosensors [6,7,8] photodetectors [9,10,11], and other current-output measurement systems, often contain a transimpedance amplifier (TIA). In [3,4,6,7,12,13,14,15], a capacitive feedback TIA (CF-TIA) has been proposed to reduce the thermal noise generated by the feedback resistor, as well as overcome difficulties in the integration of high resistance in complementary metal-oxide-semiconductor (CMOS) chips. A high value of Rdc is preferred to reduce the thermal noise currents of Rdc , it limits the maximum allowable DC input with the output voltage range of the op-amp, as in [6,7]. To overcome the shortcomings of the conventional CF-TIA, a new topology that replaces Rdc with the transistor in the feedback loop is introduced. For the CMOS implementation, the proposed topology shows the lower noise than the conventional topology by the amount of thermal noise even for the maximum DC input. The circuit is implemented with discrete components, but the frequency response model and stability analysis presented are generalized to be applicable to all CF-TIA applications and CMOS chip designs
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