JPS62203428A - Transmitter - Google Patents

Abstract

PURPOSE:To sufficiently increase an impedance at the time of off-state by inserting a diode to an internal circuit of a transformer and supplying a reverse bias voltage at standby. CONSTITUTION:In case of transmission, a base control section 61 is turned off by a TXON signal, no reverse bias voltage is fed to diodes 5a, 5b and a signal is sent through a transformer 3 to a cable. A diode at an output terminal reset by a TXD signal is turned on through a breeder resistor 63. In case of the reception, a base control section 61 is set by the TXON signal and a reverse bias voltage is fed to the diodes 5a, 5b by a power voltage E2. Thus, the diodes 5a, 5b are completely turned off and attained to the high impedance state.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a transmitting device connected to a data transmission bus and transmitting data, and in particular improves the characteristics of a transformer-insulated transceiver when not transmitting data.

(Prior art) When transmitting data using a cable, frequency-shift keying
, FSK) does not contain DC components, such as signals
Drowsiness signals may be used.

FIG. 3 is a configuration circuit diagram of a conventional transformer-insulated transceiver used for transmitting FSK signals.

In the figure, TXON is the on/off control signal, TXD
is a transmission logic signal, RXD is a reception logic signal, and L, , L2 are cable signals connected to the cable. 1 is TXO
At the track rumble section controlled by N 6, TXD 1
Complementary constant current signals are output from the two output terminals according to the binary values of the M number. That is, for one output terminal, a constant wave signal is turned on and off according to the TXD signal. 2 is a receiving section that converts the signal (g) inputted via the cable into an RXD signal, and includes a comparator. 3 is a transformer that insulates the cable from the line driving section 1 and the receiving section 2; 4 is a receiving section that converts the g signal into an RXD signal; It is a DC power supply that supplies a midpoint voltage, and is determined by taking into consideration the output voltage of the line driving section 1 and the input voltage of the receiving section 2.

The operation of the device configured as described above is as follows. When transmitting, the line driver 1 is turned on by the TXON signal, and a signal corresponding to the TXD signal is sent to the cable 1.
．． and transmits 2'FL. When performing reception, the line driving section 1 is turned off by the TXON multiplication signal, and the signal L2 is received from the cable via the receiving section 2, and the RXD
Convert it into a signal and send it.

Note that the bus used in this transmitter is a (direct) parallel connection type bus or a tree type bus using impedance matching taps.

(Problem to be Solved by the Invention) However, the line driving section 1
When one of the two output terminals of
As a result, there was a problem in that the number of transceivers connected to the bus was limited. For example, if a bus driver ICI having an open collector transistor is used in the line drive section 1, the off-characteristics of the transistor when the transmission is off are insufficient.
Sufficient high impedance cannot be obtained.

The present invention solves these problems and aims to realize a transmitting device with sufficiently high impedance when off.

(Means for Solving the Problems) The present invention that achieves the above object includes a line and a drive section that convert a transmission logic signal into a constant current signal, and a control No. 1g that controls on/off of the line drive section. , a transmitter 4A device equipped with a transformer that insulates the output signal of the line drive unit and transmits it to the cable, comprising: a diode inserted in the line connecting the line drive unit and the transformer; and a switch means for supplying a sending bias voltage to the diode and releasing the reverse bias voltage of 1 voltage when it is on.

(Function) The diode becomes high impedance to the transformer side due to the reverse bias voltage. The switch means provides reverse bias when the control signal is off.

(Example) The present invention will be explained below with reference to the drawings.

FIG. 1 is a configuration circuit diagram showing a first embodiment of the present invention. In FIG. 1, parts having the same functions as those in FIG.

In the figure, 5 is the output terminal of the line drive section 1 and the transformer 3
The diode is inserted in the line connecting the output terminal, and is connected in such a way that the output terminal is in the forward direction. Incidentally, since the line driving section 1 outputs by switching two output terminals, the diode 5 has subscripts a and b correspondingly.
to distinguish them. This diode 5 is an element that becomes sufficiently high impedance to the transformer 3 when a reverse bias voltage is applied, and the resistance before the electrostatic charge 6 is sufficiently small and high.

6 is a transistor that applies a reverse bias voltage to the diode 5; 61 is a transistor 6 that applies a reverse bias voltage to the diode 5;
62 is a DC power supply that supplies a reverse bias voltage to the diode 5 through the transistor 6; 63 is a bleeder resistor that determines a predetermined current ID to flow through the diode 5;

When the TXON signal is on, the current flows through the diode 5 on the output terminal side, which is turned off by the TXD signal.

is determined by the following formula.

■D=(vT-vDa-vDb)/2R(1) This current! . , the diode 5 on the side where the output terminal is off
is kept on. In this way, when the output terminal changes from off to on due to the TXD signal, there is no need for the diode to turn on, so a good transmission waveform can be obtained without delay.

Next, the resistance value R of the bleeder resistor 63 is determined as follows. It is preferable that the resistance value R is thicker because the power loss is smaller.
On the other hand, it is necessary to set a value that can supply a sufficient reverse bias voltage to the diode 5 when the output terminal is off. Therefore, the resistance value R is determined by the following equation.

R<'F'+"2-VRECMAX'CE
'/■OFFMAX(2'The operation of the device configured in this way will be explained below.When transmitting, TX
The pace control section 61 is turned off by the ON signal, no reverse bias voltage is supplied to the diodes 5a and 5b, and a signal is transmitted to the cable via the transformer 3. TXD
(The diode on the output terminal side, which is turned off by the i signal, is turned on by the bleeder resistor 63.

In order to perform reception 2, the pace control unit 61 is turned on by the TXON signal, and the DC voltage E2 is applied via the transistor 6.
A positive reverse bias voltage is supplied to the diodes 5m and 5b. In this way, the diodes 5m and 5b are completely turned off and are in a high impedance state.

FIG. 2 is a configuration circuit diagram showing a second embodiment of the present invention. The diode 7 is inserted with the polarity opposite to that of the diode 5 in the brown 1 embodiment. 8 is a transistor that applies a reverse bias voltage to the diode 7, 81 is a pace control section that controls the transistor 8 according to the TXON signal, and 82 is a DC power supply that supplies a reverse bias voltage to the diode 7''; The polarity is opposite. 83 is a bleeder resistor.

The circuit with this configuration operates in accordance with the first embodiment.

It should be noted that the present invention is not limited to the above-mentioned embodiments;
And one of the DC power supplies 4.62°82 of the second embodiment may be omitted (that is, if El or E2 is zero Volt).

Further, in the above embodiment, the number of output terminals of the line and the output terminal of the moving part 1 is shown as two, but it is also possible to have a single number of output terminals.

(Effects of the Invention) As explained above, according to the present invention, the diode 5 is inserted on the internal circuit side of the transformer 3 to supply a reverse bias voltage during standby, so that there is sufficient in-heating when off. I'm going to talk about it.

[Brief explanation of drawings]

The first factor is a configuration circuit diagram of the first embodiment of the present invention, FIG. 2 is a configuration circuit diagram of the second embodiment, and FIG. 6 is a connection diagram of a conventional device. DESCRIPTION OF SYMBOLS 1... Line drive part, 3... Transformer, 5... Diode, 6... Transistor (switch means), TX
D...Control number. Figure 1

Claims (1)

[Claims] A line drive section that converts a transmission logic signal into a constant current signal, a control signal that controls on/off of this line drive section, and an output signal of the line drive section that is insulated and transmitted to a cable. A transmitting device including a diode inserted in a line connecting the line driving section and the transformer, and a transmitting bias voltage is supplied to the diode when the control signal is off, and a reverse bias voltage is applied when the control signal is on. A transmitting device characterized in that it is provided with a switch means for canceling the voltage.