JP2530349B2 - Optical transmitter - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmitter that optically transmits a 2-channel analog signal using a single light emitting element.

2. Description of the Related Art This type of optical transmitter is used for optical fiber communication and optical space communication for transmitting analog signals, and the conventional optical transmitter is constructed as shown in FIG.

When the two-channel signals to be transmitted are L and R signals, the L and R signals are input to the A / D conversion circuit 3 via the first and second filters 1 and 2. The A / D conversion circuit 3 is supplied with the synchronization signal a and the bit clock signal b,
The conversion circuit 3 alternately digitally converts the L signal and the R signal based on the synchronization signal a and outputs the digital signals. The digitally converted plural bit signals are output at the timing of the bit clock signal b. Here, the synchronizing signal a is the frequency (N1 · F1) of the output signal of the oscillation circuit 4 in the first frequency dividing circuit 5 (1 /
The bit clock signal b is generated by dividing the output signal of the oscillation circuit 4 into (1 / N2) by the second frequency dividing circuit 6. However, in the case of N1 >> N2, the conventional first frequency dividing circuit 5 and second conventional frequency dividing circuit 6 independently perform the frequency dividing operation.

First signal via the output signal of the A / D conversion circuit 3 and the modulation circuit 7.
The output signal of the frequency dividing circuit 5 is frequency-multiplexed by the frequency multiplexing circuit 8, the light emitting element 9 is driven by the output signal of the frequency multiplexing circuit 8 through the driver circuit 10, and the light emitting element 9 outputs the L signal and the R signal. An optical signal 11 representing the content of the signal is transmitted.

Problems to be Solved by the Invention In such a conventional configuration, the modulation circuit 7 is required to generate the identification signal of the L and R signals, and in the frequency multiplexing circuit 8 in which the analog signal and the digital signal are mixed. ,
It is necessary to optimize the input level ratio between the analog output signal of the modulation circuit 7 and the digital signal of the output of the A / D conversion circuit 3, which is difficult in terms of circuit technology.

It is an object of the present invention to provide an optical transmitter that can be configured only with a digital circuit that can be easily adjusted.

Means for Solving the Problems An optical transmitter according to the present invention comprises an oscillator circuit for outputting a signal of frequency (N1 · F1) and a frequency divider for dividing the frequency of the output signal of the oscillator circuit into (1 / N1). 1 and the output signal of the oscillation circuit is divided into (1 / N2) [where N1 >> N2] and has a reset function by rising and falling of the output signal of the first frequency dividing circuit. The output signals of the second frequency dividing circuit and the second frequency dividing circuit are used as bit clock signals, and the first and second analog signals to be transmitted are alternately switched based on the synchronizing signal of the output signal of the first frequency dividing circuit. Of the A / D conversion circuit for performing digital conversion into a digital signal, identification signal generating means for outputting a predetermined identification signal during the digital conversion period of the first and second analog signals based on the synchronization signal, Time division in which the output signal and the output signal of the identification signal generating means are time division multiplexed A heavy circuit, when is characterized by providing a light emitting element that is driven according to the output signal of the division multiplexing circuit.

The second invention is the A / D in the configuration of the first invention.
A feature is that a modulation circuit is interposed between the output of the conversion circuit and the time division multiplexing circuit.

The third invention is the A / D in the configuration of the above-mentioned first invention.
The first modulation circuit is interposed between the output of the conversion circuit and the time division multiplexing circuit, and the second modulation circuit is interposed between the output of the time division multiplexing circuit and the light emitting element. .

Action According to the first invention, the identification signal based on the synchronization signal and the A /
The light-emitting element is driven by a signal obtained by time-division-multiplexing both signals, instead of outputting the digital signal output from the D conversion circuit by frequency-multiplexing processing as in the conventional case.

According to the second invention, the identification signal based on the synchronization signal and the A /
A light emitting element is driven by a signal obtained by performing time division multiplexing processing on a digital signal output from the D conversion circuit and modulated by the modulation circuit.

According to the third invention, the identification signal based on the synchronization signal and the A /
The digital signal output from the D conversion circuit is time-division multiplexed with the signal modulated by the first modulation circuit, and the signal that is time-division multiplexed is modulated by the second modulation circuit to emit light. Drive the element.

Embodiment An embodiment of the present invention will be described below with reference to FIGS. 1 to 3. It should be noted that components having the same functions as those of the conventional example shown in FIG.

FIG. 1 shows the first invention, and the following points are different from FIG. 4 showing a conventional example. The second frequency dividing circuit 6 for dividing the frequency (N1 · F1) of the output signal of the oscillator circuit 4 into (1 / N2) is
It has a reset function by rising and falling of the output signal of the first frequency dividing circuit 5 which divides the frequency of the output signal of the oscillation circuit 4 into (1 / N1).

Here, the frequency division ratio (1 / N2) is set so that the frequency of the bit clock signal b generated at the output of the second frequency dividing circuit 6 becomes higher than that in FIG. Also, N1 >> N2.

Reference numeral 12 is a third frequency dividing circuit as an identification signal generating means, and here, during the L signal conversion period, the frequency of the output signal of the oscillation circuit 4 is divided into (1 / N3) (N1 · F1 / N3). The signal of the frequency is output, and the signal of the frequency of (N1 · F1 / N3) is not output during the R signal conversion period. Reference numeral 13 is a time division multiplexing circuit for time division multiplexing the digital conversion output signal of the A / D conversion circuit 3 and the output signal of the third frequency dividing circuit 12, and outputs the output signals of the A / D conversion circuit 3 of a plurality of bits. After that, the signal of the third frequency dividing circuit 12 is added and output. Time division multiplexing circuit 13
The output signal of is applied to the light emitting element 9 through the drive circuit 10 and converted into the optical signal 11.

In this embodiment, since the frequency of the bit clock signal b is higher than that of the bit clock signal b in FIG. 4 as described above, the time required for a plurality of bit digital signals of the A / D conversion circuit 3 is shown in FIG. The output signal of the third frequency dividing circuit 12 is multiplexed in the shorter time portion than in the case.

With this configuration, the time division multiplexing circuit and the third frequency dividing circuit 12 can be configured by digital circuits. Time division multiplexing circuit
In 13, the adjustment of the input level as seen in the conventional frequency multiplexing circuit 8 is unnecessary, and the third frequency dividing circuit 12 has a simpler configuration than the modulating circuit 7.

On the side that receives the optical signal 11 and demodulates it, (N1F1
/ N3) frequency signal is multiplexed, and if the (N1 · F1 / N3) frequency signal is multiplexed here, the digital signal of the multiple bits is processed as the L signal component. Composed.

FIG. 2 shows the second aspect of the invention, in which an FSK modulation circuit 14 is interposed between the output of the A / D conversion circuit 3 and the time division multiplexing circuit 13 in comparison with the configuration of FIG. Noise resistance is improved.

FIG. 3 shows the third aspect of the invention, which is used as a first modulation circuit between the output of the A / D conversion circuit 3 and the time division multiplexing circuit 13.
An FSK modulation circuit 14 is interposed, and a PFM [pulse FM] modulation circuit 15 is interposed as a second modulation circuit between the output of the time division multiplexing circuit 13 and the driver circuit 10,
The noise resistance is further improved as compared with the configuration of FIG.

In each of the above embodiments, the first to third frequency dividing circuits 5, 6 and 12 use the output signal of the common oscillation circuit 4 as a signal source.
A signal can be supplied to the frequency dividing circuit 12 from a circuit different from the oscillation circuit 4. Although the identification signal generating means is the third frequency dividing circuit 12, it may be configured to generate signals of different frequencies f1 and f2 in the L signal conversion period and the R signal conversion period. At the receiving side, the frequencies f1 and f2 of this identification signal are different, and the digital signal components are L signal and R signal.
It is configured to determine which of the signals is.

As described above, according to the present invention, the identification signal based on the synchronization signal and the output signal of the A / D conversion circuit are time-division multiplexed to drive the light emitting element. Since the identification signal generating means can be configured only by a digital circuit, the circuit configuration is simplified and the circuit technology is also simplified, and the first and second analog signals can be stably received with a simple circuit configuration on the receiving side. It is a thing.

In the second invention, the digital signal input from the A / D conversion circuit to the time division multiplexing circuit is modulated through the modulation circuit,
In the invention of claim 1, since the first and second modulation circuits are provided at the input and the output of the time division multiplexing circuit to drive the light emitting element by modulating the signal, in addition to the effect of the first invention It is possible to realize high-fidelity transmission of the first and second analog signals.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the optical transmitter of the first invention, FIGS. 2 and 3 are block diagrams of an embodiment of the optical transmitter of the second and third inventions, and FIG. FIG. 4 is a block diagram of a conventional optical transmitter. L, R …… first and second analog signals, a …… sync signal, b
...... Bit clock signal, 3 ...... A / D conversion circuit, 4 ......
Oscillation circuit, 5,6 ... First and second frequency dividing circuit, 9 ... Light emitting element, 11 ... Optical signal, 12 ... Third frequency dividing circuit [identification signal creating means], 13 ... Division multiplexing circuit, 14 ... FSK modulation circuit [first modulation circuit], 15 ... PFM modulation circuit [second modulation circuit].

Claims (3)

(57) [Claims] 1. An oscillator circuit for outputting a signal of frequency (N1 · F1), a first divider circuit for dividing the frequency of the output signal of the oscillator circuit into (1 / N1), and an oscillator circuit for the oscillator circuit. The output signal is divided into (1 / N2) [where N1 >> N2] and a second frequency dividing circuit having a reset function by rising and falling of the output signal of the first frequency dividing circuit; An A / D conversion circuit for converting the output signal of the frequency dividing circuit into a bit clock signal, and digitally converting the first and second analog signals to be transmitted alternately based on the synchronizing signal of the output signal of the first frequency dividing circuit,
An identification signal creating means for outputting a predetermined identification signal during the digital conversion period of the first and second analog signals based on the synchronization signal, an output signal of the A / D conversion circuit and an output signal of the identification signal creating means. An optical transmission device provided with a time division multiplexing circuit for performing time division multiplexing processing, and a light emitting element driven according to an output signal of the time division multiplexing circuit. 2. An oscillator circuit for outputting a signal of frequency (N1 · F1), a first divider circuit for dividing the frequency of the output signal of the oscillator circuit into (1 / N1), and an oscillator circuit for the oscillator circuit. The output signal is divided into (1 / N2) [where N1 >> N2] and a second frequency dividing circuit having a reset function by rising and falling of the output signal of the first frequency dividing circuit; An A / D conversion circuit for converting the output signal of the frequency dividing circuit into a bit clock signal, and digitally converting the first and second analog signals to be transmitted alternately based on the synchronizing signal of the output signal of the first frequency dividing circuit,
Identification signal generating means for outputting a predetermined identification signal during the digital conversion period of the first and second analog signals based on the synchronization signal, a modulation circuit for modulating the output signal of the A / D conversion circuit, and the modulation An optical transmitter comprising a time-division multiplexing circuit for time-division-multiplexing an output signal of the circuit and an output signal of the identification signal creating means, and a light-emitting element driven according to the output signal of the time-division multiplexing circuit. 3. An oscillator circuit for outputting a signal of frequency (N1 · F1), a first divider circuit for dividing the frequency of the output signal of the oscillator circuit into (1 / N1), and an oscillator circuit for the oscillator circuit. The output signal is divided into (1 / N2) [where N1 >> N2] and a second frequency dividing circuit having a reset function by rising and falling of the output signal of the first frequency dividing circuit; An A / D conversion circuit for converting the output signal of the frequency dividing circuit into a bit clock signal and alternately digitally converting the first and second analog signals to be transmitted based on the synchronizing signal of the output signal of the first frequency dividing circuit,
Identification signal generating means for outputting a predetermined identification signal in the digital conversion period of the first and second analog signals based on the synchronization signal; and a first modulation circuit for modulating the output signal of the A / D conversion circuit. A time-division multiplexing circuit that time-division-multiplexes the output signal of the first modulation circuit and the output signal of the identification signal creating means; a second modulation circuit that modulates the output signal of the time-division multiplexing circuit; An optical transmitting device provided with a light emitting element driven according to an output signal of a modulation circuit.