JPH02214310A - D/a converter for digital temperature compensation type oscillator - Google Patents

Abstract

PURPOSE:To quickly make the frequency at the time of starting stable by setting the initial condition of a ROM (initial setting storage circuit) so that a temperature compensation code at rising of a power supply reaches a prescribed value. CONSTITUTION:When a power supply rises, a readout signal is outputted from a terminal CE of a power-on clear sequencer 45 to a terminal CE of a ROM 43. Thus, a compensation code at +25 deg.C is outputted to each input terminal B of multiplexers MUX1-MUX8 from output terminals DA1-DA8 of the ROM 43. Succeedingly, the power-on clear sequencer 45 brings an output terminal SEL to a high level. Thus, each output terminal X of the multiplexers MUX 1-MUX8 selects the input terminal B. Thus, a compensation code at +25 deg.C is outputted to the input terminal D of the D flip-flops DFF1-DFF8 from each output terminal X. Then an error between the oscillated frequency of the VCXO and the rated frequency is decreased.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a temperature compensated oscillator that compensates for fluctuations in oscillation frequency due to temperature changes based on digitally encoded temperature information, and particularly relates to This invention relates to a digital temperature compensated oscillator that stabilizes quickly at startup.

(Prior art) As a means of suppressing fluctuations in oscillation frequency due to temperature changes and always obtaining stable output, a memory device is used that converts temperature information into a digital signal and stores compensation control voltage codes corresponding to each unit temperature. A digital temperature compensated oscillator configured to generate a control voltage to be supplied to a voltage controlled oscillator from the code read out based on the digital signal has come into use, and from the viewpoint of accuracy and adaptability to mass production, etc. Attention has been paid.

FIG. 2 is a block diagram illustrating a configuration of a conventional digital temperature compensated oscillator and an example of its control.

In addition, as a voltage controlled oscillator, one using a crystal oscillator (VCXO) is generally used.
This will be explained below.

In this figure, the symbol l is an oscillator as a temperature sensor whose oscillation frequency changes sensitively in response to temperature.
(25℃), 40KHz, 20ppm per 1℃ (I
The oscillation frequency changes at a rate of ppm (parts per million).

The output of the sensor oscillator 1 is converted into a low-cycle pulse signal by a frequency divider 2 to control a gate circuit of a frequency counter 3.

Further, the other input terminal of this frequency counter 3 is input with a signal obtained by dividing the output of the voltage controlled crystal oscillator (VCXO) 4 to be compensated by a second frequency divider 5, and the gate circuit The number of pulses of the frequency-divided signal of this VCXO4 passing through is counted.

Since the output frequency of the temperature sensor oscillator 1 changes depending on the temperature, the VCXO4 measured by the frequency counter 3
The number of signal pulses from the sensor changes depending on the temperature and becomes a signal representing the temperature at that time.

Therefore, the result counted by the frequency counter 3 is converted into a digital signal of predetermined bits in the next address register 6, and this is input as an address to n0M7 which stores the digital value to be output corresponding to each value. do.

When an address signal is manually input to the ROM 7, the digital signal stored in each address is outputted and converted into a DC voltage by the D/A converter 8, which becomes the control voltage of the VCXO 4.

In this example, temperature information is obtained by counting the output frequency of the VCXO4 using the output pulses of the temperature sensor 1, but by changing the oscillation frequency of both or the frequency division ratio of each, the frequency counter 3 can calculate A system in which the relationship between the gate control signal and the reference pulse is reversed from the above example has also been put into practical use.

FIG. 3 is a configuration explanatory diagram showing an example of the D/A converter circuit 8 in FIG. type flip flop 11
-18 output terminals Q, respectively, and a ladder type resistor 20 consisting of at least the same number of resistors 31 to 38 connected in series. At the connection point of each series resistor of the ladder type resistor 20, each type flip-flop 11 to 18 is connected.
It is configured such that the outputs thereof are connected via voltage dividing resistors 21 to 28 of required values.

In the above configuration, the 8-pit temperature compensation code from the ROM 7 is input to each input terminal of the D-type flip-flops 11 to 18, corresponding to ~D+a, and the clock signal is input to the clock signal input terminal CK. . A digital code corresponding to the temperature information is connected to each input terminal D+r to D1.
．． , the output terminal Q of each flip-flop corresponding to the bit rlJ becomes High.
For example, the h level is 5■, and the beam is high for bit rOJ.

The W level is, for example, 0■. The output voltage from each output terminal Q is divided by a ladder type resistor 20, and the voltage corresponding to the arrangement of temperature compensation code bits rOJ rlJ is the output V of the D/A converter circuit 8. uT + is generated as a temperature compensation voltage of VCXO4.

The input bits of each flip-flop 11 to 18 are Hi.
The voltage at each output terminal Q for the gh one is Hi.
gh level, but the output is V. In uT, the D-type flip-flop I+
The highest output voltage for <, D-type flip-flop 1
The one for 8 is the lowest.

Furthermore, different DC voltages can be obtained depending on the combination of these flip-flops that produce a High output. The compensation code that can be expressed in 8 bits is ooooooooo
There are 256 ways from ~11111111.

However, in the D/A frequency converter used in the conventional digital temperature compensated oscillation 1 described above.

The reset signal is the clear terminal C of the flip-flop.
Since it is input to L, when the entire circuit is reset when the power is turned on, etc., all the output Q of each flip-flop becomes Low level, and the compensation code in which all bit values are rOJ is output to the D/A converter. join. This varies depending on the code sign and temperature expression method, but generally it is set as "00...OO-" at the lowest or highest temperature, so this code is a compensation code for either extreme temperature. Therefore, an oscillation output according to this will be output from the VCXO. - Generally, it is extremely rare for the ambient temperature to be at such an extreme level in the reset state.
"00...OO" which represents -30℃ when the temperature is ℃
If a compensation code that is It has a drawback in terms of frequency stability at startup, in that the frequency deviates significantly from the rated frequency.

From this point of view, the same applicant is Tokuton Sho 62-23.
In No. 0299, a compensation voltage that is, for example, a predetermined temperature compensation voltage (compensation voltage at an intermediate temperature of -30°C to +80°C, i.e., +25°C) is forced upon a reset such as when the power is turned on, regardless of the external temperature. We proposed a circuit that outputs a

That is, the invention according to the above application provides a preset terminal PR (shown in parentheses) in place of the clear terminal CL of the first □g flip-flop 11 shown in FIG. It is connected to each clear terminal CL of the flip-flop 12 to the eighth D-type flip-flop 18 as shown by dotted lines.

In the above configuration, when the reset input is set to High,
First D-type flip-flop l! is preset −
On the other hand, the other D-type flip-flops 12 to 18 are cleared. In this case V. In the above example, the compensation voltage output from u7 is the compensation code -100000 at room temperature 25℃.
It becomes 00°.

However, the temperature that should be set as the initial state is not uniform depending on the place where it is used.For example, in cold regions, the average temperature is low, so the initial state temperature is not +25℃ (
+5°C would be a preferred temperature; conversely, +30°C would be a preferred initial temperature in tropical regions.

When the circuit according to the above application is used in a cold region or a tropical region, the wiring of the PR terminals of the D-type flip-flops 11 to 18 must be changed in order to change the initial setting temperature.

However, this type of product must be mass-produced in advance.
Since the use of the circuit is often determined in accordance with the customer's requirements, the above-mentioned circuit requires wiring changes each time depending on the usage environment, which increases the number of man-hours before shipping and is extremely complicated. Moreover, there is a possibility that a connection error or the like may occur depending on the case.

Furthermore, if this circuit is made into an IC, it becomes impossible to change the wiring.

(Object of the Invention) The present invention has been made in order to eliminate the drawbacks of the D/A converter circuit in the conventional digital temperature compensated oscillator as described above. A digital temperature sensor that not only improves startup stability by minimizing deviations in the oscillation frequency of the VCXO, but also allows various initial condition settings to be set by simple means without changing wiring connections. It is an object of the present invention to provide a compensated oscillator D/A converter.

(Summary of the Invention) In order to achieve the above object, the D/A converter of the digital temperature compensated oscillator of the present invention uses a compensation code indicating the value to be output as the control voltage of the voltage controlled oscillator under initial conditions, for example, when the power is turned on. , by using means for writing the compensation code into the ROM and switching between this compensation code and a compensation code based on actual temperature information.

The device is characterized in that it is configured to operate using the compensation code from the ROM immediately after the power is turned on, and from the other side after a predetermined period of time has elapsed.

(Example) Below, a D/A converter of a digital temperature compensated oscillator according to the present invention will be described in detail.

FIG. 1 is an explanatory diagram of the configuration of a D/A converter circuit used in the digital temperature compensated oscillator of the present invention. This invention is a further development of the invention of No. 62-230299. Therefore, the explanation of the structure and operation of the entire temperature compensated crystal oscillation circuit will be omitted since it overlaps with the explanation of FIG. 2.

This D/A converter circuit 40 includes D-type flip-flops DFF I to DFF8 and each type flip-flop D
A conventional circuit consisting of a ladder type resistor 42 connected to the output terminals Q of FF 1 to DFF 8, multiplexers MUXI to MUX 9 with 2 manual outputs, a ROM (memory circuit for initial setting) 43, and a power-on clear sequencer 4
It has a configuration with 5 added.

Each of the flip-flops DFF1 to DFF8 has an input terminal for inputting each temperature compensation code, a clock input terminal C for inputting a clock signal, and an output terminal Q. Then, according to the clock signal input to the input terminal CK, the signal input to the D terminal is output from the Q terminal.

The ladder resistor 42 is a flip-flop DFF.
It is composed of resistor groups 2R1-R1, 2R2-R2, . . . 2R8-R8 that divide the output voltage of I-DFF8 into different values.

The power-on clear sequencer 35 clears the multiplexer each time the power is turned on, and simultaneously operates to output a predetermined signal from each output terminal of the ROM 43.

Each flip-flop DFF from ROM7 in Figure 2
8-bit temperature compensation code D input to DFF1 to DFF8
Among I-Ds, the temperature compensation code D is the most significant bit, and D is the least significant bit.

The temperature compensation code that can be expressed with 8 pits is ooooo.

There are 256 codes from OO to (1) 11111, and the compensation code at room temperature 25°C is the 128th 100000.
00 and number! By providing a preset terminal PR in the D-type flip-flop DFF I, the most significant bit is set to rlJ as an initial condition, and the other D-type flip-flops are set to rol. Therefore, the compensation code at reset is r10000000J or 2
The temperature is set at 5°C.

Each output terminal D1 to D of the ROM33 is a multiplexer M.
It is connected to each input terminal A of the UXI-MUX8. The clock output terminal CK is connected to the input terminal A of the ninth multiplexer MUX9, and its output terminal
Each input terminal CK of flip-flops DFF1 to DFF8
It is connected to the. 1st to 8th multiplexer MUX
The output terminals of I to MUx8 are D-type flip-flops DF.
It is connected to each input terminal of F1 to DFF8.

Each output terminal Q of the D-type flip-flop DFFI-DFF8 is connected to each resistor group 2R1-R constituting the ladder resistor 42.
1, 2R2-R2, . . . 2R8-R8 are respectively connected to the outputs of the ladder resistor 42. Ll? is connected to the control input terminal of VCXO4 as a compensation voltage.

The output terminals DA1 to D88 of the ROM33 are connected to the input terminals B of the multiplexers MUXI to MUX8, respectively, and the terminals CE of the power-on clear sequencer are connected when the power is turned on.
A preset signal (initial setting compensation code) is output based on the signal output from.

Output terminal CE of power-on clear sequencer 45 1.
t To the input terminal CE of ROM 43, and to the output terminal SE
L is connected to the input terminal SEL of multiplexer MUXI-MUX9 (7), and output terminal CK is connected to the input terminal of multiplexer MUX9 (7).

The gist of the present invention having the above configuration is that the compensation code corresponding to the voltage to be applied at the time of power-on is set in advance by R.
By providing a multiplexer that selects either the output from the ROM 43 or the output generated via the frequency counter 3 as the temperature compensation code written in the OM 43 and supplied to each of the flip-flop circuits, the ambient temperature can be adjusted. The point is that the error between the oscillation frequency at startup and the rated frequency is reduced regardless of the value. Further, by simply writing different compensation codes in the ROM 43 depending on the usage environment of the digital temperature compensated oscillator, settings can be easily made according to the usage environment of the digital temperature compensated oscillator.

Next, the present invention will be explained in detail.

First, in steady-state oscillation operation, each output terminal
Output to each input terminal of FFI to DFF8. That is, R
The 8-pit compensation cord of OM7 is connected to each output terminal, ~
D, the first to eighth multiplexers MUXI to MUX
When the input signal is input to each input terminal A of 8, each output terminal
Output to each input terminal of FF8. continue.

When the clock signal output from the output terminal CK to the ninth multiplexer MUX9 is changed from Low level to Hjgh level, the signal from the output terminal X to the input terminal CK of each of the flip-flops DFF1 to DFF8 also becomes High. , each type flip-flop DFF
The signals applied to each input terminal of I to DFF8 become outputs (compensation codes) from each output terminal Q as they are.

At this time, each input terminal R9, 1-R of the ladder resistor 42
, N8 are applied to resistors 2R1 to 2R8, respectively.
The voltage is divided by R1-R8, and from the output terminal V ou7 to V
CX O41m applied Sarel.

Next, the operation when the power is turned on will be explained.

In this case, the initial setting condition in the ROM 43 is 25.
If the compensation code is stored in the case of °C,
This will be explained as an example.

When the power is turned on, the CE of power-on clear sequencer 45
Since a read signal is output from the terminal to the CE terminal of the ROM 33, a compensation code at +25° C. is output from each output terminal DAI-DA8 of the ROM 43 to each input terminal B of the multi-break fMUX1-MLIX8. Next, the power-on clear sequencer 45 outputs the output terminal SEL.
In order to set it to High level, multiplexer MUXI
~MtJX8 (7) Each input terminal SEL is also High.
), so that each output terminal X of the multiplexer MUXI-MUX8 selects the input terminal B. For this reason.

From each output terminal X to D type flip-flop DFF 1 to D
A 25° C. compensation code will be output to the input terminal of FF8.

Next, when the CK terminal output of the power-on clear sequencer 45 changes from Low level to High level, it becomes High level.
The h level signal is output to each input terminal CK of the D-type flip-flops DFFI to DFF8 via the ninth multiplexer 9, and a compensation code at 25° C. is output from each output terminal Q to the input terminal of the ladder resistor 42. R,,1
-R,,8, and finally output terminal ■. A compensation voltage at 25° C. is output from u7 to the control voltage terminal of vcxo4. In this example, at normal temperature 2 at reset
The reason for applying the compensation voltage at 5°C to vcxo4 is
Since 25°C is the center of the digital temperature compensated oscillator's compensation temperature range -30°C to +80°C, no matter what the external temperature is within the compensation temperature range when the power is turned on, the temperature will be 25°C. This is because it is possible to reduce the error between the oscillation frequency of the VCXO and the rated frequency.

Also, if you want to set the compensation code at power-on to a code with a temperature other than 25°C, you can change the temperature written to the ROM 33 according to the bit value corresponding to the code. Alternatively, if the temperature is set to the respective average temperature when used in a high area, it is possible to respond to the ambient temperature more quickly.Also, if the compensation temperature range is different from the above example, for example -4
When the temperature is between 0°C and +60°C, a code corresponding to the intermediate temperature loC may be generated.

Furthermore, in implementing the present invention, it is applicable not only to the above-mentioned 8-bit case, but also to any pit, and not limited to D-type flip-flops, but any circuit element having a similar function. It is obvious that any material may be used.

(Effects of the Invention) As described above, according to the digital temperature compensated oscillator of the present invention, the initial conditions of the ROM (initial setting memory circuit) are set so that the temperature compensation code at power-up becomes a predetermined value. This structure prevents the temperature compensation voltage of the VCXO from becoming a voltage corresponding to the extremes of the set temperature range in the initial state such as when the power is turned on.
Furthermore, it is possible to bring the VCXO into a steady state at the rated frequency in a short time, which is effective in quickly improving the stability of the frequency at startup.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an example of a D/A converter circuit used in the digital temperature compensated oscillator of the present invention, FIG. 2 is an explanatory block diagram of a conventional digital temperature compensated oscillator, and FIG. 3 is a block diagram of a conventional digital FIG. 2 is an explanatory diagram of a block configuration of a D/A converter used in a temperature compensated oscillator. XO) 5... Frequency divider 6... Address register 7... ROM 8... D/A converter M
UX I-MUX9...Multiplexer DFFI-D
FF8...D type flip-flop 2R1~2R8...
・Resistance R1-R8...Resistance 40...D/A conversion circuit 42...Ladder type resistor 43...ROM
(Initial setting memory circuit) 45...Power-on clear sequencer Patent applicant Hitoshi Suzuki, Patent attorney, Toyo Tsushinki Co., Ltd.

Claims (2)

[Claims] (1) Temperature information is obtained using a temperature sensor oscillator whose oscillation frequency changes depending on the ambient temperature, a voltage controlled oscillator, and a frequency counter that uses the output of one of the oscillators as a gate signal to measure the oscillation frequency of the other. A digital temperature compensated oscillator that performs temperature compensation by converting a temperature compensation code created in response to the digital signal into an analog voltage using a D/A converter and then using it as a control voltage for the voltage controlled oscillator. A digital temperature compensated oscillator D/A converter, characterized in that the D/A converter includes a memory circuit for setting an initial state when power is turned on. (2) The D/A converter includes a flip-flop circuit corresponding to the number of bits of the temperature compensation code, and a ladder resistor that adds the outputs of each flip-flop circuit in series;
A multiplexer circuit for selecting either the output from the initial setting memory circuit or the output generated via the frequency counter as a temperature compensation code to be supplied to each of the flip-flop circuits. D/A of the digital temperature compensated oscillator according to claim (1)
converter.