JP3478098B2 - Probe circuit for bus - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to IEEE 1394.
Apply to a bus probe circuit suitable for use in a bus analyzer, etc. used for analysis of packet communication, etc.
Particularly, it relates to improvement of a probe circuit having high input impedance using a high speed operational amplifier.

[0002]

2. Description of the Related Art IEEE 1394 is a communication protocol for high-speed communication of multimedia information such as moving images, still images, voices and characters with general-purpose AV devices such as computers, peripheral devices and digital video cameras. Then, communication is performed by the high-speed serial bus, and the packet data to be communicated is transmitted and received at regular time intervals. In developing a device having such a 1394 bus interface, it is necessary to observe the waveform on the bus for debugging. Therefore, in the past, the digital oscilloscope was controlled to measure the waveform of the bus, and the waveform that caused the trigger was displayed in the center of the screen.

FIG. 2 is an explanatory diagram of a conventional bus waveform measurement. The 1394 bus has four signal lines TPA ± and TPB ±
Are used to transmit signals. The arithmetic circuit inputs a common signal (TPA ++ TPA-) of a pair of TPA + and TPA- and a differential signal (TPA + -TPA-), and a common signal (TPB + of TPB + and TPB-) input through the buffer circuit. + TPB-) and differential signal (TPB-
+ -TPB-) is calculated and the waveform is output. The physical layer PHY is 1
A physical circuit that drives signals on the 394 bus. The link layer LINK takes charge of the interface between the transaction layer and the physical layer. The transaction layer is 1
It is a layer that controls the entire 394 bus and defines the request / response protocol, and performs the read / write and lock functions. To facilitate observation with an oscilloscope, a trigger circuit 30 for generating a trigger signal and a control circuit 40 for generating a control signal are provided in the bus probe circuit.

In the device constructed as described above, 13
The 94 bus device is analyzed for each mode such as bus reset, cycle period, and configuration.

[0005]

However, in measuring the waveform of each signal with an oscilloscope, the arithmetic circuit does not affect the original signal waveform, so that it is necessary to satisfy low capacitance and high impedance, and several hundreds of them are required. The first problem is that it is necessary to secure a very wide frequency band because it is necessary to observe a high-speed differential signal of Mbit / s.

Therefore, there is a method of realizing a differential operation circuit by using a high-speed IC design method, but there is a problem that it becomes difficult to manufacture it at low cost. There is also a method of realizing a differential operation circuit using FETs, but there is a problem that it is difficult to improve gain accuracy and suppress temperature drift to a small level. Further, there is a method of realizing a differential operation circuit by using a high-speed operational amplifier, but in general, a high-speed operational amplifier has a narrow input common voltage range and has a small DC common voltage (1.165 to 2.515V) of a large amplitude like a 1394 bus signal. There is a problem that it is difficult to calculate a signal in which a differential voltage of amplitude (0.230 to 0.530 V) is superimposed and to divide it into a differential component and a common component.

Further, in the debugging work, there is a second problem that the customer's request to know the raw signal waveform before calculation is satisfied rather than displaying only the differential component and the common component.

The present invention solves such a problem, and a first object thereof is to calculate a signal in which a small amplitude differential voltage is superimposed on a large amplitude DC common voltage with high speed and high accuracy. A probe circuit for a bus having a processing circuit is provided. A second object is to provide a probe circuit for a bus that enables smooth debugging by displaying signals before and after calculation on a waveform display device.

[0009]

In order to achieve the first object, a probe circuit for a bus according to claim 1 of the present invention comprises:
For analysis of packet communication specified by IEEE1394
A bus probe circuit that requires two signal lines
There are two sets, and in each set of signal lines, a buffer circuit is provided for each signal line of the bus that transmits a bit string signal of a predetermined speed by a differential voltage, and a signal of this buffer circuit is input to generate a differential voltage . Differential signal arithmetic circuit for arithmetic operation, and the buffer
Common signal that inputs the signal of the circuit and calculates the common voltage
No. operation circuit and power supply voltage were input and shifted to the positive side
The power supply voltage supplied to said common signal calculating circuit and the buffer circuit, provided a voltage regulator for supplying a power supply voltage of the same power supply potential to the positive and negative sides to the differential signal operation circuit
It is characterized in that that.

[0010]

According to the first aspect of the present invention, when the buffer circuit and the common voltage calculation circuit are configured to shift the power supply voltage to the common voltage side, the common signal can be calculated with low distortion. Specifically , since the common voltage on the 1394 bus is a positive voltage, the power supply voltage may be shifted to the positive voltage side. Further, if the differential voltage calculation circuit is configured to have the same power supply potential on both positive and negative sides, the differential signal to be observed can be calculated without distortion.

In order to achieve the second object, the bus probe circuit according to claim 2 of the present invention is the bus probe circuit according to claim 1.
In the invention, each output signal of the buffer circuit and the difference
The differential voltage motion signal calculating circuit, the inputs of the common voltage of the common signal arithmetic circuit is characterized by providing a selection circuit for outputting to the display recording device to select them. With this configuration, the signal waveform before the calculation and the signal waveform after the calculation can be displayed on the display recording device, so that the debugging work can be smoothly performed.

[0013]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. In the figure, a buffer circuit 1 is a circuit of low capacitance and high input impedance, which does not affect the signal voltage of a signal line, and operates, for example, a high-speed current feedback operational amplifier as a voltage follower circuit. The common signal calculation circuit 2 calculates a common signal (TPA ++ TPA-) of a pair of TPA + and TPA- of the 1394 bus and a common signal (TPB ++ TPB-) of a pair of TPB + and TPB-. Differential signal arithmetic circuit 3
Is a differential signal of a pair of TPA + and TPA- of the 1394 bus
(TPA + -TPA-) and the differential signal of the pair of TPB + and TPB- (T
Calculate PB + -TPB-).

The voltage regulator 5 supplies a stabilizing voltage of +7 V and -3 V to the buffer circuit 1 and the common signal arithmetic circuit 2, and supplies a stabilizing voltage of ± 5 V to the differential signal arithmetic circuit 3. The DC-DC converter 6 supplies electric power insulated from the main power source to the voltage regulator 5. The main power source is, for example, a power source of a bus analyzer having a bus probe circuit as an attachment.

The display device 7 is for observing waveforms, and for example, an oscilloscope is used, but a recording device such as a recorder may be used. The buffer amplifier 8 takes out the signal before the operation of the common signal operation circuit 2 and the differential signal operation circuit 3, and inputs the signal of the buffer circuit 1 here. The signal before calculation is TPA of 1394 bus
+, TPA-, TPB +, TPB-. Selection circuit 9
Is a circuit for selecting a signal waveform before calculation and a signal waveform after calculation for display on the display device 7. The signal waveform of the buffer amplifier 8 is used for the signal waveform before the calculation and the common signal calculation is performed for the signal waveform after the calculation. The signals of the circuit 2 and the differential signal calculation circuit 3 are selected.

The operation of the apparatus thus configured will be described. First, a configuration for calculating a common signal with low distortion will be described. When selecting a large-amplitude positive-side common voltage like a 1394 bus signal and a small-amplitude differential voltage superimposed on this common voltage for calculation, the buffer circuit 1 and the common-signal calculation circuit 2 using a high-speed operational amplifier When all the differential signal arithmetic circuits 3 are driven by the same positive and negative power supplies, there is a problem that waveform distortion occurs due to the limitation of the input common voltage of the high speed operational amplifier.

Since the common signal amplitude of the 1394 bus is only the positive voltage amplitude, the buffer circuit 1 and the common signal calculation circuit 2 do not need to calculate the negative voltage waveform. Therefore, the buffer circuit 1 and the common signal operation circuit 2 can be configured to shift the power supply voltage to the positive side and realize an appropriate input common voltage range. For example, when the power supply voltage range of the operational amplifier is 10V, the negative power supply is set to -3V and the positive power supply is set to + 7V. As a result, the common signal can be calculated with low distortion.

By the way, since the differential signal has both positive and negative amplitudes, when a power supply whose power supply voltage is shifted to the positive side is used, the differential signal operation circuit 3 causes waveform distortion in the negative side amplitude. Therefore, the voltage regulator 5 uses a power supply voltage different from the power supply for the buffer circuit 1 and the common signal calculation circuit 2 for the power supply of the differential signal calculation circuit 3 so that the observed differential signal can be calculated without distortion. . For example, when the power supply voltage range of the operational amplifier is 10V, the negative power supply is set to -5V and the positive power supply is set to + 5V.

In the above embodiment, the common signal operation circuit 2 and the differential signal operation circuit 3 are provided by the buffer amplifier 8.
However, the present invention is not limited to this, and the signal of the buffer circuit 1 may be directly input to the selection circuit 9. Also,
Since the number of input channels of the display device 7 is limited to four here, the selection circuit 9 is provided. However, the number of input channels of the display device 7 may be eight or more and the selection circuit 9 may be omitted.

[0020]

As described above , according to the present invention,
It has the following effects.

According to the first aspect of the present invention, if the buffer circuit and the common voltage calculation circuit are configured to shift the power supply voltage to the common voltage side, the common signal can be calculated with low distortion. Specifically , since the common voltage on the 1394 bus is a positive voltage, the power supply voltage may be shifted to the positive voltage side. Further, if the differential voltage calculation circuit is configured to have the same power supply potential on both positive and negative sides, the differential signal to be observed can be calculated without distortion.

According to the second aspect of the present invention, since the signal waveform before the calculation and the signal waveform after the calculation can be displayed on the display recording device by the selection circuit, the raw data of the bus of the device under test can be observed. Yes, you can debug smoothly.

[Brief description of drawings]

FIG. 1 is a configuration block diagram showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram of conventional bus waveform measurement.

[Explanation of symbols]

1 buffer circuit 2 Common signal arithmetic circuit 3 Differential signal operation circuit 7 Display recording device 9 Selection circuit

Continuation of the front page (56) References JP-A-11-120093 (JP, A) JP-A-11-161520 (JP, A) JP-A-7-12871 (JP, A) Junichi Furumura, IEEE 1394 High Performance -Outline of Serial Bus, Interface, Japan, CQ Publishing Co., Ltd., April 1, 1996, Vol. 22, No. 3, p. 114-123 Yoshihiro Onishi, Fundamentals of Amplifier Circuits and Their Analysis, Transistor Technology, Japan, CQ Publishing Co., Ltd., September 1, 1996, Volume 33. No. 9, p. 265-279 Kameyoshi Yanase, In-depth research on current-feedback OP amplifier, Transistor technology, Japan, CQ Publishing Co., Ltd., Dec. 1, 1994, Vol. 31, No. 12, p. 277-281 Toshio Yamamoto, How to use Oshiroshi Corp. (2), Transistor Technology, Japan, CQ Publishing Co., Ltd., October 1, 1986, Volume 23, No. 10, p. 481-482 (58) Fields surveyed (Int.Cl. ⁷ , DB name) G06F 11/00 G06F 13/00 G01R 13/28 JSTPLUS file (JOIS)

Claims (2)

(57) [Claims] 1. A packet defined by IEEE 1394
A bus probe circuit used for communication analysis , which has two sets of two signal lines, and each set of signal lines has a bus line that transmits a bit string signal of a predetermined speed by a differential voltage. The buffer circuit provided and the signal of this buffer circuit are input and the differential voltage is calculated.
A differential signal operation circuit, a common signal operation circuit that inputs a signal from the buffer circuit to calculate a common voltage , a power supply voltage that is input , and a power supply voltage that is shifted to the positive side
A probe circuit for a bus , comprising: a buffer circuit; and a voltage regulator that supplies the common signal operation circuit and supplies a power supply voltage of the same power supply potential to the differential signal operation circuit on both positive and negative sides. 2. Output signals of the buffer circuit and the difference
2. The circuit for bus probe according to claim 1, further comprising a selection circuit for inputting a differential voltage of the dynamic signal calculation circuit and a common voltage of the common signal calculation circuit, selecting the selected voltage and outputting the selected voltage to the display recording device. .