JP3271617B2 - Pickup circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pickup circuit, and more particularly to a pickup circuit for a signal reproducing device.

[0002]

2. Description of the Related Art Referring to FIG. 3 showing a conventional pickup circuit, this pickup circuit converts an optical signal by a laser beam reflected from a disk (not shown) into a current signal by a photodiode 11 and feeds it back. Circuit 28
And an operational amplifier comprising a differential circuit 17 and a push-pull circuit 25, and converts the voltage signal into a voltage signal. Photodiode 11
Since most of the current Ip generated by the current flows through the feedback circuit 28, the gain of the operational amplifier is determined by the configuration of the feedback circuit 28, and the feedback circuit 28 is usually configured by a filter circuit.

The node Vc of the pickup circuit is connected to the base of the transistor 13 of the differential circuit 17, and the base of the transistor 14 is connected to the constant power supply 18. Potential Vref of constant power supply 18 and transistor 1
3, the base-emitter voltage VBE (13) and the transistor 14 base-emitter voltage VBE (14) represent the potential at the node Vc, where Vc = Vref-VB
E (14) + VBE (13), which is almost equal to Vref
Becomes Usually, since the photodiode 11 has an epitaxial substrate configuration, the current Ip generated by the photodiode 11 is
1 flows from the N pole to the P pole. At this time, the node VB (output terminal 29) is given by: VB = Vref + RFB * Ip (1) The current Ip is the sum of the current flowing through the load 26 and the current supplied from the push-pull circuit 25.

[0004] Ideally, the output voltage at the output terminal 29 is
It does not fall below the reference voltage as shown in FIG.

[0005]

However, in the signal reproducing apparatus, it is necessary to detect the position of the disk in order to reproduce the signal accurately. More specifically, for example, four pickup circuits are used to correct the focus distance to the disk, and two pickup circuits are used to track a circular orbit signal. As the control signal, the output voltage when dark light is incident (the voltage Vref of the constant power supply is used because the current Ip is substantially zero according to Equation 1) is used.

However, in reality, when the light changes from bright to dark due to a load condition and a phase compensation capacitor (not shown) inside the operational amplifier, an undershoot occurs in the output voltage, and the output voltage undershoots around the reference voltage. There was a problem that a settling time was required until it became stable.

Therefore, an object of the present invention is to solve the above problems,
An object of the present invention is to provide a pickup circuit having a short settling time.

[0008]

A pickup circuit according to the present invention comprises: a first power supply line to which a high potential is supplied; a second power supply line to which a low potential is supplied; an output terminal; An emitter of a first bipolar transistor of one conductivity type and an emitter of a second bipolar transistor of a conductivity type opposite to that of the first bipolar transistor are connected between a power supply line and the second power supply line. A push-pull circuit connected to the output terminal to output a pickup output signal;
A photodiode that receives an optical signal and converts the optical signal into an electric signal, and a feedback circuit that generates an input signal by feeding back the pickup output signal of the output terminal in response to the electric signal of the photodiode. A differential circuit that receives the input signal and amplifies the input signal; and a pickup circuit that receives the differential output signal of the differential circuit by the push-pull circuit and outputs the pickup output signal. A clip circuit is provided for clamping the base potential of the second bipolar transistor at a predetermined potential so as to prevent undershoot of the potential of the base of the transistor.

The differential circuit of the pickup circuit according to the present invention connects the emitter of a third bipolar transistor receiving the input signal at a base and the emitter of a fourth bipolar transistor receiving a constant potential at a base. The clip circuit of the pickup circuit of the present invention may further comprise a fifth bipolar transistor receiving the constant potential as a base, and a collector between the fifth bipolar transistor and the first power supply line. And the emitter of the fifth bipolar transistor may be connected to the base of the second bipolar transistor, and the push-pull circuit of the pickup circuit of the present invention may include: A differential output signal of the differential circuit is received at a base, and an emitter is connected to the first bipolar transistor. A sixth bipolar transistor connected to the base of the second bipolar transistor; and a seventh bipolar transistor receiving the differential output signal of the differential circuit at the base and connecting the emitter to the base of the second bipolar transistor. You can also.

[0010]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a circuit diagram of a pickup circuit according to an embodiment of the present invention.

Referring to FIG. 1, a pickup circuit according to an embodiment of the present invention includes a first power supply line VCC supplied with a high potential and a ground line GN supplied with a low potential as a ground potential.
D, an output terminal 29, and a push terminal connected between the power supply line and the ground line GND, and connecting the emitter of the NPN bipolar transistor 23 and the emitter of the PNP bipolar transistor 24 to the output terminal 29 to output a pickup output signal. A pull circuit 25, a photodiode 11 that receives the optical signal PD and converts the optical signal into a current, and an output terminal 2 corresponding to the current flowing through the photodiode 11
9, a feedback circuit 28 that feeds back the pickup output signal to generate an input signal, a differential circuit 17 that receives the input signal, amplifies the input signal, and push-pulls the differential output signal of the differential circuit 17 A clip circuit 32 is provided for clamping the base potential of the bipolar transistor 24 at a predetermined potential so as to prevent undershoot of the potential of the base of the bipolar transistor 24 when receiving the pickup output signal upon receipt of the signal.

The clipping circuit 32 has an NPN bipolar transistor 31 receiving the constant potential Vref of the constant voltage source 18 at its base, and a load resistor 30 connected between the collector of the bipolar transistor 31 and the power supply line VCC. , The emitter of the bipolar transistor 31 is connected to the base of the bipolar transistor 24 of the push-pull circuit 25.

That is, the pickup circuit of the present invention
A clip circuit 3 is added to the conventional pickup circuit shown in FIG.
2 is added.

The transistor 31 in the clip circuit 32
Has a base connected to a constant voltage source, and an emitter connected to a node VA that is lower than the output terminal 29 (node VB) by a base-emitter voltage VBE (24) of the transistor 24, so that the potential of the node VA is It does not spread beyond the base-emitter voltage VBE (31) of the transistor 31. Therefore, the lower limit of the potential of the node VA is limited. Similarly, since the potential of the output terminal 29 (node VB) is a potential obtained by adding the voltage VBE (24) between the base and the emitter of the transistor to the potential of the node VA, a lower limit is imposed on the output voltage. As a result, as shown in FIG. 2, the output undershoot is substantially eliminated, so that the settling time can be shortened.

According to the simulation result, when the reference voltage of the constant voltage source was set to 2.5 V, the output potential was lowered to 1.8 V due to undershoot, but the output potential was improved to 2.4 V, and the settling time was also improved from 70 ns to 40 ns. Was done.

[0016]

As described above, the pickup circuit of the present invention has an effect that the settling time can be shortened and high-speed reading can be performed since the output undershoot is substantially eliminated.

[0017]

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a pickup circuit according to an embodiment of the present invention.

FIG. 2 is an operation waveform of the pickup circuit shown in FIG.

FIG. 3 is a circuit diagram of a conventional pickup circuit.

FIG. 4 is an operation waveform showing the principle of a pickup circuit.

5 is an operation waveform of the conventional pickup circuit shown in FIG.

[Explanation of symbols]

Reference Signs List 11 Photodiode (PD) 12, 19, 22 Constant current 13, 14, 20, 23, 31 NPN bipolar transistor 15, 16, 21, 24 PNP bipolar transistor 17 Differential circuit 18, 27 Constant voltage source 25 Push-pull circuit 26 Load 28 Feedback circuit 29 Terminal 30 Resistance 32 Clip circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04R 3/00 310 H03K 17/04 H03K 17/66

Claims (8)

(57) [Claims] A first power supply line to which a high potential is supplied; a second power supply line to which a low potential is supplied; an output terminal; and a first power supply line and a second power supply line. The emitter of a first bipolar transistor of one conductivity type and the emitter of a second bipolar transistor of a conductivity type opposite to that of the first bipolar transistor are connected to the output terminal to generate a pickup output signal. A push-pull circuit for outputting, a photodiode for receiving the optical signal and converting the optical signal into an electric signal, and an input signal for feeding back the pickup output signal of the output terminal in response to the electric signal of the photodiode. A differential circuit that receives the input signal and amplifies the input signal; and the push-pull circuit receives a differential output signal of the differential circuit and the pickup circuit. A pickup circuit for outputting a loop output signal, comprising: a clip circuit for clamping a base potential of the second bipolar transistor at a predetermined potential so as to prevent an undershoot of the potential of the base of the second bipolar transistor. And the pickup circuit. 2. The semiconductor device according to claim 1, wherein the differential circuit includes an emitter of a third bipolar transistor receiving the input signal at a base,
2. The pickup circuit according to claim 1, wherein the pickup circuit is configured by connecting the emitter of a fourth bipolar transistor receiving a constant potential to a base. 3. The clip circuit includes: a fifth bipolar transistor receiving the constant potential at a base;
And a load resistor connected between the collector of the bipolar transistor and the first power supply line. The emitter of the fifth bipolar transistor is connected to the base of the second bipolar transistor. Claim 1
Or the pickup circuit according to 2. 4. The push-pull circuit receives a differential output signal of the differential circuit at a base, and connects a sixth bipolar transistor having an emitter connected to a base of the first bipolar transistor. 4. The pickup circuit according to claim 1, further comprising: a seventh bipolar transistor receiving a differential output signal at a base and connecting an emitter to a base of said second bipolar transistor. 5. The method according to claim 1, wherein the first bipolar transistor is N
5. The pickup circuit according to claim 1, wherein said second bipolar transistor is a PNP transistor. 6. The transistor according to claim 1, wherein said third bipolar transistor and said fourth bipolar transistor are NPN bipolar transistors.
The described pickup circuit. 7. The semiconductor device according to claim 6, wherein the sixth bipolar transistor is P
5. The pickup circuit according to claim 1, wherein said seventh bipolar transistor is an NP transistor, and said seventh bipolar transistor is an NPN transistor. 8. The pickup circuit according to claim 1, wherein said feedback circuit comprises a resistor.