Wide bandwidth photoelectric converting circuit

Claim 1

A photoelectric converting circuit comprising: a light receiving element for receiving incident light and producing a current signal corresponding to the amount of incident light, said light receiving element having an internal capacitance; current-to-voltage converting means for converting said current signal produced by said light receiving element into a voltage signal at an output terminal, said voltage signal having a cut-off frequency at which its magnitude is substantially reduced; an active circuit component connected between said light receiving element and said current-to-voltage converting means for receiving said current signal produced by said light receiving element and supplying a current to said current-to-voltage converting means, said active circuit having an internal resistance and a low input impedance as seen by said light receiving element; bias resistance connected to said active circuit means; the parallel combination of said internal capacitance of said light receiving element, said internal resistance of said active circuit and said bias resistance forming a load resistance of the current signal of said light receiving element, said internal resistance being substantially smaller than said bias resistance so that said load resistance is substantially the value of said bias resistance thus increasing the value of said cut-off frequency to expand the bandwidth of said photoelectric converting circuit.