JPH08211437A - Oscillation circuit for camera - Google Patents

Abstract

PURPOSE: To provide an oscillation circuit which is inexpensive and excellent in space efficiency and accuracy by using a quartz oscillator and a CR oscillation circuit together and adjusting the CR oscillation circuit by a quartz oscillation circuit. CONSTITUTION: The CR oscillation circuit 3 generates and amplifies resonance frequency for an externally attached resistance R and a capacitor C0 formed on an integrated circuit. A 1st frequency divider circuit 3a frequency-divides output from the circuit 3 and generates and outputs a clock to a control circuit 1. The quartz oscillation circuit amplifies oscillation frequency of an externally attached quartz oscillation element Xtal and a 2nd frequency divider circuit 4a frequency-divides the output from the circuit 4 and generates and outputs the clock to the control circuit 1. Then, the control circuit 1 acts based on any clock outputted from the 1st or the 2nd frequency-divider circuit 3a or 4a selected by a clock selection circuit 5. The quartz oscillator and the circuit 3 are used together, the clock for controlling a shutter is supplied from the circuit 4, and the circuit 3 is adjusted by the circuit 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oscillator circuit of a camera.

[0002]

2. Description of the Related Art In recent years, a camera equipped with a microcomputer has been widely known. A digital circuit such as a microcomputer operates only when a clock is supplied from an oscillation circuit using a ceramic oscillator or a crystal oscillator, or a CR oscillation circuit.

In a camera, usually only a ceramic oscillator is used as an oscillation source in view of cost and accuracy, but a ceramic oscillator and a crystal oscillator are used together, or only a CR oscillation circuit is used. And so on.

[0004]

However, when a ceramic oscillator and a crystal oscillator are used, the accuracy is sufficient (ceramic oscillator ± about 1%, crystal oscillator ± about 1000).
ppm), both elements are expensive, and 2
It is not suitable for compact cameras because it requires space to mount two elements.

On the contrary, although the CR oscillator circuit consumes less power and is inexpensive, even if the CR oscillator circuit is accurately adjusted due to changes in the surrounding environment such as temperature, a drift error of about ± 5% will appear. I will end up. This error is
In particular, since it appears as variations in exposure when driving the shutter, it causes overexposure and underexposure, which is a fatal drawback. In addition, an adjustment process is required at the time of manufacturing, and when an EEPROM (electric eraseable programmable read only memory) is used for adjustment, further cost increase and mounting space are required.

An object of the oscillator circuit of the present invention is to realize an oscillator circuit which is inexpensive, space-efficient, and accurate.

[0007]

In order to solve the above-mentioned problems, in the oscillation circuit of the camera of the present invention, the first oscillation circuit and the second oscillation whose oscillation accuracy is higher than that of the first oscillation circuit. A circuit and adjusting means for adjusting the first oscillation circuit,
A timer means, an activation means, and a control means for adjusting the first oscillation circuit by the adjustment means based on the outputs of the timer means and the second oscillation circuit according to the output of the activation means. There is.

According to the second aspect of the invention, the second oscillation circuit is used for controlling the drive of the shutter.

[0009]

The crystal oscillator and the CR oscillator circuit are used together, and the shutter control clock is supplied from the crystal oscillator circuit. Also CR
The crystal oscillator circuit is used to adjust the oscillator circuit.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of a camera adjusting device of the present invention.
Shown in A central processing circuit (hereinafter referred to as CPU) 10 centrally controls the camera. A control circuit 1 exists in the CPU 10, and the control circuit 1 controls various operations of the camera based on a program stored in the ROM 1a in advance. Read-only memory (hereinafter referred to as ROM) 1a
In addition to the program, is also stored the data table etc. necessary for the operation of the camera. Also random access
The memory (hereinafter referred to as RAM) 1b is used by the control circuit 1 for temporary storage and calculation. The display circuit 2 is a display panel 2a
Causes various displays such as error display.

The CR oscillating circuit 3 generates and amplifies a resonance frequency between the externally attached resistor R and the capacitor C0 formed on the integrated circuit. The first frequency dividing circuit 3a divides the output to generate a clock and outputs it to the control circuit 1. The crystal oscillating circuit 4 amplifies the oscillation frequency of the externally attached crystal oscillating element Xtal, and the second frequency dividing circuit 4a divides its output to generate a clock and outputs it to the control circuit 1. Here, the oscillation frequency of the crystal oscillating device Xtal is 32.768 kHz. The control circuit 1 operates based on one of the clocks selected by the clock selection circuit 5 and output by the first frequency dividing circuit 3a or the second frequency dividing circuit 4a.

The oscillation frequency of a crystal oscillator used in a camera is generally about 32 kHz. Quartz crystal oscillators with higher frequencies consume less power and place a heavy burden on the power supply, and are therefore not often used. The second time required for shutter control is about 1/500 second and 250 / second in a compact camera. Therefore, it can be said that the frequency is sufficiently high to control the shutter even at 32 kHz. .

Next, the oscillation operation of the CR oscillation circuit 3 will be described with reference to FIG. Inverter INV1 to inverter I
When the power source up to NV3 is turned on, the control circuit 1 turns on only the switch SW1 through the clock selection circuit 5.
In this state, assuming that the output point C of the inverter INV3 is at a high potential (hereinafter abbreviated as "H"), the capacitors C0 and C1 are charged via the resistor R. The potential at the input point A of the inverter INV1 rises as the capacitors C0 and C1 are charged, and eventually exceeds the threshold voltage of the inverter INV1 (threshold voltage Vth in FIG. 2). Then, the potential of the output point B of the inverter INV2 becomes "H", but since the voltage is divided by the capacitors C0 and C1, the inverter INV1
The potential at the input point A of Vth becomes Vth + Vdd × Cg / (Cg + C1). Here, when the potential of the output point B of the inverter INV2 becomes “H”, the potential of the output point C of the inverter INV3 becomes “L”, so that the capacitor C1 is connected via the resistor R.
And the electric charge stored in the capacitor C0 is discharged.
The potential at the input point A of the inverter INV1 is the capacitor C
1 and capacitor C0 as they discharge,
Eventually, it becomes lower than the threshold voltage of the inverter INV1 (threshold voltage Vth in FIG. 2). Then, the potential at the output point B of the inverter INV2 becomes "L", but since the voltage is divided by the capacitors C1 and C0, the inverter INV1
The potential at the input point A of Vth becomes Vth-Vdd * Cg / (Cg + C1). Here, when the potential at the output point B of the inverter INV2 becomes "L", the potential at the output point C of the inverter INV3 becomes "H". By repeating this operation, the CR oscillation circuit 3 of this embodiment oscillates and its oscillation cycle T increases.
Is

[0014]

[Equation 1]

[0015] Here, the case where the switch SW1 is turned on and the capacitor C1 is selected as the capacitor for oscillation has been described, but the same operation can be performed with other combinations of capacitors.

Regarding the capacitance of the capacitor, the capacitor C2 is twice as large as the capacitor C1, and the capacitor C3 is the capacitor C1.
4 times, and the capacitor C4 is 8 times as large as the capacitor C1. By combining these, a capacity of 1 to 15 times that of the capacitor C1 can be obtained. This capacity is
It is changed based on the value set in the register D in M1b. The adjustment value can be selected from 1 to 15, and the multiple of the adjustment value of the capacitor C1 becomes the combined capacitance.

Although the CR oscillation circuit 3 starts oscillating immediately after the power is turned on, the crystal oscillation circuit 4 usually requires a time of several hundred milliseconds to several seconds from the time when the power is turned on until the oscillation starts. Therefore, by prohibiting the shutter operation during this period, malfunction of the shutter is prevented.

Next, a method of adjusting the CR oscillation circuit 3 will be described with reference to FIG. When the photographer presses the start switch 11, the CPU 10 executes the adjustment routine of the CR oscillation circuit 3 shown in FIG. Prior to the adjustment of the CR oscillation circuit 3, the clock selection circuit 5 selects the CR oscillation circuit 3 and supplies its own clock from the CR oscillation circuit 3. Then R
The intermediate value 8 is assigned to the register D provided at a predetermined address of the AM 1b (S01), and the adjusting circuit 6 is set to select the capacitance corresponding to the register D (S02). Then, the timer 7a is set to 0 (S03) and the timer 7b is set to 10 (S04). When the setting of the timer is completed, the timer 7a and the timer 7b are simultaneously started (S05). The timer 7b waits until the time is up (S06), and when the time is up, the timer is stopped (S07).

If the count value of the timer 7a is greater than 747 (S08) and less than 780 (S09), it is considered that the optimum capacitor has been selected, and this routine is terminated. If the count value of the timer 7a is 747 or less and the register D is 15 or less in S08, the capacity of the capacitor is insufficient (S10).
Is added to increase the capacity (S11), and the process returns to S02. If the count value of the timer 7a is 780 or more and the register D is 15 or less in S08, the capacity of the capacitor is insufficient (S10). Therefore, 1 is added to the register D to increase the capacity (S11), and S02 is set. Return. Timer 7a in S08
If the count value of is greater than or equal to 780 and register D is greater than 1 (S12), subtract 1 from register D (S1
3) and returns to S02.

If D is 15 in S10 or D is equal to 1 in S12, the capacitance of the capacitor cannot be adjusted and cannot be used as the system clock. Therefore, the display circuit 2 causes an error to be displayed on the display panel 2a. The power supply to the circuit is stopped (S14). As described above, the oscillation frequency of the CR oscillation circuit can be adjusted to a value suitable for the system.

In this embodiment, two timers 7a and 7b are used. However, during execution of FIG. 3, since the software instruction is executed based on the clock generated by the CR oscillation circuit 3, no operation ( NO
If a command such as P) that does not otherwise affect is repeated a predetermined number of times and the time is measured by the timer 7a, the timer 7b is unnecessary.

In this embodiment, the value of the timer 7a is 78.
When the value is 0 or more and D is 0, the system power supply is stopped, but the crystal oscillation circuit continues to have a low oscillation frequency for a while after the oscillation starts, so if the value of the timer 7a is large, it will continue for a predetermined time. The adjustment may be performed again after waiting.

[0023]

As described above, the crystal oscillator and the C
Since the R oscillation circuit is also used and the clock for controlling the shutter is supplied from the crystal oscillation circuit, highly accurate image capturing can be performed. Moreover, since the CR oscillation circuit is adjusted by the crystal oscillation circuit, an adjustment circuit and process are not required, which is advantageous in terms of space and contributes to cost reduction.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram of a CR oscillator circuit according to an embodiment of the present invention.

FIG. 3 is a flowchart showing a CR oscillation circuit adjustment routine of the present invention.

[Explanation of symbols]

 3 CR oscillation circuit (first oscillation circuit) 4 Crystal oscillation circuit (second oscillation circuit) 6 Adjustment circuit 7a, 7b Timer 1 Control circuit 8a Shutter

Claims (3)

[Claims] 1. A first oscillating circuit, a second oscillating circuit having oscillation accuracy higher than that of the first oscillating circuit, adjusting means for adjusting the first oscillating circuit, timer means, and starting means. And a control means for adjusting the first oscillation circuit by the adjustment means based on the outputs of the timer means and the second oscillation circuit according to the output of the starting means. circuit. 2. The second oscillating circuit is used when drive control of a shutter is performed.
The oscillator circuit of the camera described in. 3. A first oscillating circuit and a second oscillating circuit having an oscillation accuracy higher than that of the first oscillating circuit, wherein the second oscillating circuit is used for controlling drive of a shutter. The oscillator circuit of the camera, which is characterized in that