High voltage generating circuits

Abstract: A high-voltage generating circuit suitable for a light receipting circuit includes a pulse oscillating circuit, a current drive circuit, a first capacitor, a second capacitor, a Cockcroft-Walton circuit, a low-pass filter. The pulse oscillating circuit produces a train of repetitive pulses. The current drive circuit produces a train of repetitive pulses which are in phase opposite to the train of repetitive pulses. The first capacitor couples the current drive circuit with the first input terminal of the Cockcroft-Walton circuit. The second capacitor couples the pulse oscillating circuit with the second input terminal of the Cockcroft-Walton circuit. The Cockcroft-Walton circuit boost the pulse voltage applied between the first and second inputs to produce a high direct current voltage. The low-pass filter removes the ripple components of the high direct current voltage. The Cockcroft-Walton circuit can be formed with a small number of circuit components.

Description: Background of the Invention The present invention relates to a high-voltage generating circuit suitable for a light receiving circuit used in an optical transmission device. Description of the Related Art Some light receiving circuits used in an optical transmission device include avalanche-type photo diodes which act as an light receiving element. This kind of avalanche-type photo diode requires a high-voltage generating circuit to produce a high direct-current voltage, for example, 80 to 120 volts, to cause the electron multiplying function inside the avalanche-type photo diode. Since a prior art high-voltage generating circuit employs a transformer, it has been difficult to flatten a printed circuit board mounting a light receiving circuit. In order to overcome such a problem, it is known from U.S. patent 4, 992, 922 to use a high-voltage generating circuit employing a Cock-croft-Walton circuit instead of the transformer. This U.S. patent describes an example of a light receiving circuit including the avalanche-type photo diode. The light receiving circuit described in the above U.S. Patent also uses high voltage generating circuit with a Cockcroft-Walton circuit which can operate on the same power supply as that for the pulse generating circuit. However, it has been desired to reduce the number of circuit components of the above-mentioned high-voltage generating circuit to realize more miniaturization and simplification of the light receiving circuit. In the US 4 236 199 also a voltage boosting and rectifying circuit is disclosed. In contrast to the previously mentioned voltage generator, the voltage boosting and rectifying circuit is driven by two pulse trains of opposite phase. Therefore the voltage variation is doubled in comparison to the generator of the US 4 992 922. Therefore it is possible, to decrease the number of capacitors and diodes to one half in such a voltage boosting circuit, like the Cockcroft-Walton circuit mentioned before. However, the oscillator will be more complicated, because two pulse trains with pulses of opposite phase must be generated, instead of only the one pulse train according to the US 4 992 922. The disclosure of the US 4 236 199 teaches a circuit for generation of a pulse train and buffer means. The buffer means not only serve for buffering, but also for generating at its two outputs the two pulse trains with opposite phase. The number of electronic devices necessary for a high voltage generating circuit according to the technical teaching of US 4 236 199 therefore is still large. Summary of the Invention The object of the invention is to provide a high-voltage generating circuit which can be formed of a small number of circuit components. A high-voltage generating circuit according to the present invention is described in claim 1. Further improvements of the invention are described in the dependent claims. Brief Description of the Drawings Fig. 1 shows a circuit diagram of a high-voltage generating circuit according to a preferable embodiment of this invention; and Fig. 2 shows pulse wave-forms at inputs of the Cockcroft-Walton circuit shown in the Fig. 1. Detailed description of the preferred embodiment The high-voltage generating circuit according to an embodiment of the present invention will described in Fig. 1 and Fig. 2. Fig. 1 shows a circuit diagram of the high-voltage generating circuit for providing a direct-current voltage to avalanche-type photo diode (APD) 6. The high-voltage generating circuit comprises a current-driven pulse oscillating circuit 3, a first capacitor 7a, a second capacitor 7b, a Cockcroft-Walton circuit 4, and a low-pass filter 5. The current- driven pulse oscillating circuit 3 is formed of a pulse oscillating circuit 1 and a current drive circuit 2. The pulse oscillating circuit 1 includes C-MOS inverters 23 to 26, capacitor 13, resistors 11 and 12, and outputs a train of pulses A with a predetermined oscillation frequency to the output line 100, as shown in Fig. 2. The predetermined oscillation frequency is proportional to the time constant determined by a product of the resistor 12 and the capacitor 13. The inverters 23 and 24 act as a current drive circuit. The current driving circuit 2 is formed of C-MOS inverters 21 and 22. The current driving circuit 2 also amplifies the output pulse of the C-MOS inverter 25, and outputs a train of repetitive pulse which is in phase opposite to the repetitive pulses from the inverter 25 in the pulse oscillating circuit 1, to the output line 102. The output pulses of the both pulse oscillating circuit 1 and the current driving circuit 2 have an amplitude of 3 to 5 volts. The capacitor 7a is connected between the output of the pulse oscillating circuit 1 and the input node A of the Cockcroft-Walton circuit 4. The capacitor 7b is connected between the output of the current drive circuit 2 and the input node B of the Cockcroft-Walton circuit 4. The capacitor 7a and 7b have a capacitance value of, for example, 0.04 to 0.05 µF. The Cockcroft-Walton circuit 4 is formed of a resistor 41 grounding the input node B, and a plurality of boosting stage, each being formed of two diodes and two capacitors. The Cockcroft-Walton circuit 4 receives the pulses input by way of the capacitors 7a and 7b from the pulse oscillating circuit 1 and the current drive circuit 2. The capacitors used in the Cockcroft-Walton circuit 4 have a capacitance value of, for example, 0.04 to 0.05 µF. The low-pass filter 5 is formed of a resistor R and a capacitor C, and removes the ripple components of the high direct-current voltage from the Cockcroft-Walton circuit 4. In an operation of the high-voltage generating circuit of the invention, as shown in Fig. 2, a pair of the repetitive pulses which are in the opposite phase from each other are output to the input nodes A and B of the Cockcroft-Walton circuit through the capacitors 7a and 7b. Therefore, a pulse with an amplitude twice as that of each of the pulses output from current-driven pulse oscillating circuit 3 can be applied between the nodes A and B of the Cockcroft-Walton circuit 4. As described above, since a pulse voltage larger than that in a conventional high-voltage generating circuit is applied to the Cockcroft-Walton circuit, if a high direct-current voltage with the same amplitude is desired, the number of the voltage boosting stage in the Cockcroft-Walton circuit can be decreased, for example, to a half. The high-voltage generating circuit according to the invention should not be limited to the present embodiment. It is apparent that other modifications can perform without departing from the scope of the present invention determined by the terms of the claims (Art. 69 EPC).

Claims: High-voltage generating circuit comprising a pulse generator (1), an amplifying circuit for amplifying pulse trains, and a voltage-boosting and rectifying circuit (4), wherein the pulse generator (1) has a plurality of inverters (24, 25, 26) connected in series and generates a first train of pulses (C') and a second train of pulses (C") which are in phase opposition to each other, the amplifying circuit has a first current drive circuit (23, 24) for amplifying the first train of pulses (C') and a second current drive circuit (21, 22) for amplifying the second train of pulses (C"), and the high-voltage generating circuit further comprises a first capacitor (7a) having a first and second terminal, the first terminal being connected to the first current drive circuit (23, 24), and a second capacitor (7b) having a first and second terminal, the first terminal being connected to the second current drive circuit (21, 22), wherein each of the first and second current drive circuits has a pair of inverters (23, 24; 21, 22) and one (24) of the inverters in one (23, 24) of the current drive circuits is common to one of the inverters (24, 25, 26) of the pulse generator (1). Circuit according to claim 1, wherein said voltage-boosting and rectifying circuit (4) comprises a Cockcroft-Walton circuit. Circuit according to claim 1 or 2, wherein said current drive circuits (23, 24; 21, 22) comprise a plurality of C-MOS inverters connected in parallel with each other. Circuit according to claim 1, wherein said pulse generator (1) includes the first current drive circuit (23, 24). Circuit according to claim 4, wherein said pulse generator (1) and said second current drive circuit (21, 22) form a current-drive pulse generator (3). Circuit according to one of claims 1 to 5, wherein said circuit further comprises a low-pass filter (5) connected to said voltage-boosting and rectifying circuit (4) for reducing ripple components of the high direct current voltage from said voltage-boosting and rectifying circuit (4). Circuit according to one of claims 1 to 6, wherein said low-pass filter circuit (5) is connected to an avalanche-type photo diode (6).

Inventors: ISHIMURA KATSUHIRO, TAKEDA KAZURO, ISHIMURA, KATSUHIRO, TAKEDA, KAZURO, Ishimura, Katsuhiro, c/o Oki Elec. Ind. Co., Ltd., Takeda, Kazuro, c/o Oki Elec. Ind. Co., Ltd.
Applicants: OKI ELECTRIC IND CO LTD, OKI ELECTRIC INDUSTRY CO., LTD.
Application year: 1992
Main classification: H02M7
IPC codes: H04B10, H02M7, H02M9, H02M3