JPH10334603A - Analog monitor circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease the number of pins for the output of a monitor. SOLUTION: This circuit has amplifiers 10 and 11 which form the single output for the signal from an AC signal generating source 31 after the differential amplification, and an amplifier 12 which obtains the difference between the single output from the amplifier 11 and a reference DC bias VR' and forms the single output at the same time. The signal current (i) of the single output from the amplifier 12 undergoes voltage conversion by using a load resistor R' and a bias VR" of a ground reference. The signal after the voltage conversion is monitored and outputted as the difference from the ground.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an analog monitor circuit applicable to a read system of a read / write amplifier circuit of, for example, an FDD (floppy disk drive).

[0002]

2. Description of the Related Art FIG. 2 shows a block configuration of a read system 40 of a general FDD read / write amplifier circuit.

In FIG. 2, a signal (reproduced signal) generated by an AC signal generating source 31 which is a reproducing head for reading a signal from a floppy disk, for example, is supplied to an initial amplifier 50 via input terminals 33 and 34. Is entered.
The first-stage amplifier 50 takes a differential amplifier type in order to handle a reproduced signal that is a minute signal. The output of the amplifier 50 is converted into a single output and input to the filter 52 at the next stage. Here, the reason why the output of the amplifier 50 is intentionally made to be a single output is that the circuit scale is reduced by the differential filter format. The output of the filter 52 is output from the output terminal 38 as output data after a logical operation is performed by a predetermined logic circuit 53.

Here, although a single signal is handled in the filter 52, the signal is already amplified by the amplifier 50, and the differential is substantially obtained by using the same reference DC bias as the amplifier 50. Because, so-called P
Deterioration of power supply rejection ratio (SRR) basically does not occur.

When the output of the amplifier 50 is monitored by such a circuit, the output of the amplifier 50 is converted into two monitor outputs by a monitor output generating amplifier 51.
This is taken out from the monitor output terminals 36 and 37.

The configuration of the monitor circuit for generating the monitor output is usually of a differential type as shown in FIGS. 3 and 4 for canceling external noise. 3 and 4 corresponding to those in FIG. 2 are denoted by the same reference numerals as those in FIG. 2, and descriptions thereof will be omitted.

In FIGS. 3 and 4, amplifiers 60 and 61 are shown.
Corresponds to the amplifier 50 of FIG. 2, and the output of the amplifier 61 is a single output. The output terminal of the amplifier 61 is connected to the terminal 35 via a resistor R.
5 is connected to the filter 52 of FIG.

In the example of FIG. 3, the output terminal of the amplifier 61 is connected to the non-inverting input terminal of the differential amplifier 62, and the inverting input terminal of the differential amplifier 62 has a reference DC bias V _R '.
Is applied. In the differential amplifier 62, a difference between the output signal of the amplifier 61 and the reference DC bias V _R ′ is obtained, and the differential output is made again to generate the monitor output. The reference DC bias V _R ′ is usually generated based on a Vcc-dependent bias V _R such as Ｖ Vcc for optimization of the bias. In this circuit, a voltage dividing resistor having the same resistance value r, an operational amplifier 65, and a transistor T
r, the reference DC bias V _R ′ becomes Vc
It is generated from the c-dependent bias V _R.

On the other hand, in the example of FIG. 4, two signals of the output signal of the amplifier 61 and the above-mentioned reference DC bias V _R ′ are output, and a kind of differential output is performed to provide a monitor output. . In the case of FIG. 4, similarly to FIG. 3, the reference DC bias V _R 'is generated based on the Vcc dependent bias V _R.

[0010]

The method of FIGS. 3 and 4 is a differential output method which is strong against external noise such as PSRR. At least two pins for monitor output are required.

However, at present, while the number of pins has been increased due to the increase in the scale of the IC, it is necessary to reduce the number of pins for cost reduction. It is desired to reduce the number of pins.

The present invention has been made in view of such circumstances, and has as its object to provide an analog monitor circuit capable of reducing the number of pins.

[0013]

According to the present invention, a signal from an AC signal source is differentially amplified and then converted to a single output, and the single output and the reference DC bias are differentially converted to a single output. The above-described problem is solved by converting a single output signal current into a voltage using a load resistance on a ground-referenced bias, and monitoring and outputting the output signal after the voltage conversion as a differential with respect to the ground.

That is, in the present invention, the signal and the reference D
By taking the differential with the C bias, a signal current from which the common mode noise component has been removed can be obtained. Further, the signal current is converted into a voltage using a load resistor on a ground-based bias, so that the common mode noise is reduced. A signal voltage from which noise has been removed can be obtained. By taking the difference between the signal of this signal voltage and the ground, a single output monitor output is obtained. This makes it possible to make the monitor output a single output without deteriorating the PSRR of the original differential signal.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

The analog monitor circuit according to the embodiment of the present invention is applicable to, for example, a read system 40 of a read / write amplifier circuit of an FDD (floppy disk drive) as shown in FIG. The monitor output is generated when the output of the amplifier is monitored by such a type of circuit. In the monitor circuit of the present embodiment,
About monitor output, PSRR (power supply rejecti
On-ratio) etc., it is possible to reduce the number of pins by using a single output.

Here, in order to output a single differential output as described in the prior art, for example, only one of the signals may be extracted. However, in the prior art arrangement, since the monitor output is produced based on the internal bias V _R, when viewed based on a different reference potential, such as an external ground reference, just the common mode supply ripple such as noise Cannot be removed, resulting in deterioration of PSRR and the like.

Therefore, in the embodiment of the present invention, the analog monitor circuit is configured as shown in FIG.
Convert the monitor output into a single output while considering R, etc.
The number of pins can be reduced. In addition, among the constituent elements in FIG. 1, those corresponding to FIG. 2 are denoted by the same reference numerals as those in FIG. 2, and description thereof will be omitted.

In FIG. 1, the amplifiers 10 and 11 correspond to the amplifier 50 of FIG. 2, and the output of the amplifier 11 is a single output. The output terminal of the amplifier 11 is connected to a terminal 5 via a resistor R, and this terminal 5 is connected to the filter 52 shown in FIG.

In the example shown in FIG. 1, the output terminal of the amplifier 11 is connected to the non-inverting input terminal of the differential amplifier 12, and the inverting input terminal of the differential amplifier 12 has a reference DC bias V _R '.
Is applied. The differential amplifier 12 takes the difference between the output signal of the amplifier 11 and the reference DC bias V _R ′, and extracts only one of the differential outputs. The reference DC bias V _R ′ is generated based on the １ ／ Vcc-dependent bias V _R for bias optimization. In this circuit, the reference DC bias V _R ′ is reduced to 上 記 Vc by the voltage dividing resistor having the same resistance r, the operational amplifier 15 and the transistor Tr.
It is generated from Vcc dependent bias V _R such c.

As described above, in the analog monitor circuit of the present embodiment shown in FIG. 1, the circuit 2 enclosed by the broken line in FIG.
Other than 0, the configuration is the same as that of the conventional technique.

In the circuit of this embodiment, the output of the amplifier 11 is once received by the amplifier 12, and the amplifier 12 takes a difference between the signal and the reference DC bias V _R '. Then, the signal current i from which the common mode noise is removed is obtained.

Here, when the signal current i is converted into a voltage using a load resistance R ′ on a ground-based bias V _R ″, a signal voltage from which common mode noise has been removed can be obtained. In the circuit of the present embodiment, the single output signal can be output from the monitor output terminal 6 as a monitor output. When actually monitoring this signal, it is sufficient to look at the difference from the ground.

As described above, according to the circuit of the present embodiment, it is possible to realize single output monitoring in consideration of PSRR and the like. That is, according to the embodiment of the present invention, the analog monitor pin that has output differentially can be changed to single output (ground reference). In addition, although the output is a single output, by taking the differential with the ground, the level becomes the same level as the differential output such as PSRR, and the signal does not deteriorate.

[0025]

As is apparent from the above description, in the present invention, the signal from the AC signal source is differentially amplified, then converted to a single output, and the difference between the single output and the reference DC bias is obtained. Further, by making a single output, the signal current of the single output is subjected to voltage conversion using a load resistance on a ground-based bias, and the output signal after the voltage conversion is monitored and output as a differential with the ground,
The monitor output can be made a single output without deteriorating the PSRR of the original differential signal, so that the number of monitor output pins, which conventionally required two pins, can be reduced by one pin.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating a schematic configuration of an analog monitor circuit according to an embodiment of the present invention.

FIG. 2 is a block circuit diagram showing a schematic configuration of a read system of a read / write amplifier circuit of an FDD (floppy disk drive) to which an analog monitor circuit is applied.

FIG. 3 is a circuit diagram showing a configuration example of a conventional analog monitor circuit.

FIG. 4 is a circuit diagram showing another configuration example of a conventional analog monitor circuit.

[Explanation of symbols]

6 monitor output terminals, 10, 11, 12 amplifiers,
31 AC signal source, 33, 34 input terminal

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shun-ichiro Takahashi 5-1 Noguchi Kita, Kokubu-shi, Kagoshima Sony Kokubu Corporation

Claims (2)

[Claims] A first differential amplifying means for differentially amplifying a signal from an alternating-current signal generating source and outputting a single output; and a single output from the first differential amplifying means and a reference DC.
The second to take the differential with the bias and make a single output
And a voltage converting means for converting a single output signal current from the second differential amplifying means to a voltage using a load resistance on a ground-based bias. An analog monitor circuit for monitoring and outputting an output signal as a differential with respect to ground. 2. The analog monitor circuit according to claim 1, wherein said reference DC bias is generated based on a power supply voltage dependent bias.