KR950010889B1 - Frequency selecting circuit - Google Patents

Abstract

The circuit consists of a gate circuit which changes output logic, a frequency voltage converter which converts the voltage level of horizontal frequency, a comparator (U1) which compares the output voltage with a reference voltage, an analog switch which is connected with a resistor, a 4 channel analog multiplexer which inputs the output of the comparator, a non-inverting terminal of comparators (U2), (U3) which inputs the output of the comparator, a transistor (Q1) which has base, connected with the output of the comparator (U1), and a collector, connected with the output of the comparator (U2), and a transistor (Q2) which has a base, connected with the output of the comparator (U2), and a collector, connected with the output of the comparator (U3).

Description

Frequency selection circuit

1 is a block diagram of a conventional frequency selection circuit.

2 is a frequency selection circuit diagram according to the present invention.

* Explanation of symbols for main parts of the drawings

10: gate circuit 20: frequency voltage converter

30: 4-channel analog multiplexer 40: Analog switch

R1 ~ R7: Resistor Q1, Q2: Transistor

U1, U2, U3: Comparator

The present invention relates to a frequency selection circuit, and more particularly, to a frequency selection circuit configured to accurately select a frequency by using a transistor for a horizontal frequency added to increase the resolution in a monitor.

In the prior art, an apparatus for selecting a desired frequency in a monitor having a multi-mode frequency includes a gate circuit (B) by operating horizontal and vertical frequencies in the VGA (31KHz) and SVGA (33.5KHz) modes as shown in FIG. For example, using the IC 74LS86; 10), the 4-channel analog multiplexer 30 and the analog switch 40 were operated to operate the VGA mode (31.5 KHz) and the SVGA (35.5 KHz).

For example, when the frequency voltage converter 20 is low L, the select terminal S0 is low, and the select terminal S1 is low, the horizontal and vertical modes are 70 * 350 mode, and the frequency voltage converter 20 is low. (L), when select stage S0 is low and select stage S1 is high, the horizontal and vertical modes are 720 * 400 mode, frequency voltage converter 20 is low, select stage S0 is high, select. When step S1 is low, the frequency mode selection is made such that the horizontal and vertical modes are 640 * 480 mode.

However, in the conventional technique, two frequencies (VGA and SVGA) can be selected as one comparator during operation of the circuit. However, when there are three or more frequencies added, there is a problem in that selection is difficult.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an object of the present invention is to provide a frequency selection circuit that can accurately select a multi-mode horizontal frequency in a simple configuration using a transistor.

Hereinafter, embodiments of the frequency selection circuit according to the present invention will be described in detail with the accompanying drawings.

2 is a frequency selection circuit diagram according to the present invention, in which a gate circuit 10 whose output logic is changed by receiving horizontal and vertical frequencies H and V, and a horizontal scan voltage output from the gate circuit 10 are shown in FIG. A frequency voltage converter 20 for converting to a level, a comparator U1 for generating an output by comparing the voltage output from the frequency voltage converter 20 with a reference level, and an analog switched by the output of the comparator U1. In the circuit including the switch 40 and the four-channel analog multiplexer 30 in which the output logic of the select terminals S0 and S1 is selected by the output level of the comparator U1, the comparator U1. Parallel two stages of comparators U2 and U3 connected to an output side of the comparator U1 to generate an output comparing the output level of the comparator U1 and the reference level, respectively, and the outputs of the comparators U2 and U3. Transistors Q1 and Q2 that are switched in accordance with logic to select a frequency Was composed hayeoseo included. More specifically, the comparator U2 is provided with reference voltage providing resistors R1 and R2, and the comparator U3 is provided with reference voltage providing resistors R4 and R5.

In addition, the output of the comparator U2 is provided with a reference voltage providing resistors R4 and R5 in the analog switch 40.

In addition, the output of the comparator U2 is connected to the analog switch 40 and to the base of the transistor Q1 through a resistor R3, and the collector of the transistor Q1 is connected to the analog switch 40. In addition, the resistor R7 is connected to the output side of the comparator U1 and to the four-channel analog multiplexer 30. In addition, the output of the comparator U3 is connected to the analog switch 40 and is connected to the base of the transistor Q2 through a resistor R6, and the collector of the transistor Q2 is connected to the comparator U2. It is connected to the output terminal.

On the other hand, the reference voltages of the comparators U1, U2, and U3 are set differently, for example, when the reference voltage A applied to the comparator U1 is set to 5.5V, the reference voltage of the comparator U2 is set. (B) is set to 13V, and the reference voltage C of the comparator U3 is set to 15V.

In the present invention, the above-described set voltage will be described as an example.

First, the horizontal frequency H is converted into a voltage level by the frequency voltage converter 20 at the horizontal and vertical frequencies input to the gate circuit 10.

The output of the frequency voltage converter 20 is output after being compared with the reference voltage A in the comparator U1. In the circuit configuration, the comparator U1 includes amplifying means for amplifying the compared value twice. .

Accordingly, the output of the frequency voltage converter 20 is input to the comparators U2 and U3 by any one of two modes of 5.5 V or less and 5.5 V or more by the comparator U1.

TABLE 1

TABLE 2

Therefore, the comparators U2 and U3 are compared by the reference voltages B and C, respectively, and their values are output. The output values are the frequency voltage converter 20 in the A mode as shown in Tables 1 and 2. The output of the comparator U1 is low, the output of the comparator U2 is low, the output of the comparator U2 is low, and the four-channel analog multiplexer 30 is selected in A mode. When the output of the frequency voltage converter 20 is 6V in the B mode, the output of the comparator U1 becomes high to operate the operation control pin of the 4-channel analog multiplexer 30 to stop the operation of the 4-channel analog multiplexer 30. Then, the output of the comparator U2 is low and the output of the comparator U3 is low to operate U-1 of the analog switch circuit 40 to select the B mode.

In the C mode, the output of the frequency voltage converter 20 becomes 7V, the output of the comparator U1 becomes high, the output of the comparator U2 becomes high, and the transistor Q1 is turned on to output the comparator U1. Is made low, and the output of the comparator U3 is made low by the reference voltage.

Therefore, as a result, the output of the comparator U1 goes low and only the comparator U2 goes high to operate the U-2 of the analog switch 40 to select the C mode.

In the D mode, the output of the frequency voltage converter 20 becomes 8V and the output of the comparator U1 becomes 16V and is input to the comparators U2 and U3. Accordingly, the outputs of the comparators U2 and U3 are both high, and the transistors Q1 and Q2 are operated to make the comparators U1 and U2 input to the analog switch 40 low. Therefore, only the comparator U3 is made high to operate the U-3 of the analog switch 40 to select the D mode.

As such, each frequency mode is selected according to the output logics of the comparators U1, U2, and U3, thereby making accurate frequency selection.

As described above, the present invention has the effect of accurately selecting three, four or more frequencies by a concise circuit configuration.

Claims (1)

A gate circuit that receives horizontal and vertical frequencies and whose output logic changes, a frequency voltage converter for converting the horizontal frequency output from the gate circuit to a voltage level, and compares the voltage output from the frequency voltage converter with a reference level. A circuit comprising a generated comparator, an analog switch switched by the output of the comparator, and a four-channel analog multiplexer in which the output logic of the select stage is selected by the output level of the comparator, the output of the comparator U1. It is applied to the four-channel analog multiplexer 30 and is connected to the analog switch 40 through a resistor, the output of the comparator (U1) of the comparator (U2), (U3), the constant reference voltage is applied to the inverting terminal A base of the transistor Q1 which is input to a non-inverting terminal and whose output of the comparator U2 is connected to a collector terminal of the comparator U1 Connected to the analog switch 40, the output of the comparator U3 is connected to the base of the transistor Q2 connected to the collector terminal of the comparator U2, and to the analog switch 40. And a VGA output of the 4-channel analog multiplexer 30 is configured to be connected to the signals U-1, U-2, and U-3 selected by the analog switch 40. .