JPS6330804B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a temperature compensated voltage controlled oscillator suitable for semiconductor integrated circuits.

Voltage controlled oscillators used in high frequency circuits such as VTRs are generally integrated into an integrated circuit together with other circuits, and are integrated with high density to simplify the external parts of the integrated circuit.

FIG. 1 is a block diagram showing the configuration of a conventional voltage controlled oscillator, and FIG. 2 is a vector diagram of signals at points A to F in FIG.

In FIG. 1, 1 indicates the entire integrated circuit. 2 is an input terminal, 3 is an input terminal that amplifies the input signal and adjusts the phase.
An inverting amplifier that inverts the phase by 180 degrees, 4 a phase inverter that inverts the phase by 180 degrees, 5 a phase shifter that shifts the phase,
6 is a voltage control amplifier whose output size is controlled by the voltage input from the voltage control input terminal 7;
is an adder that adds together the output of the phase shifter 5 and the output of the voltage control amplifier 6, and 9 is an output terminal. The above is configured inside the integrated circuit, and a phase shifter 10 is provided outside and connected between the input and output terminals of the integrated circuit.

In the above configuration, the input signal input from the input terminal 2 is amplified by inverting the phase by 180 degrees in the inverting amplifier 3, and its output is input to the phase inverter 4 and the phase shifter 5. The signal input to the phase inverter 4 has its phase inverted again by 180 degrees and is input to the next voltage control amplifier 6. The signal input to the voltage control amplifier 6 is input to the adder 8 with its magnitude controlled by the voltage input to the voltage control input terminal 7. On the other hand, the signal input to the phase shifter 5 is input to the adder 8 with its phase shifted. The adder 8 adds the output signals of the voltage control amplifier 6 and the phase shifter 5 and outputs the sum to the output terminal 9. The signal that enters the phase shifter 10 outside the integrated circuit from the output terminal 9 is further shifted in phase, output, and input to the input terminal 2. The circuit oscillates when the phase difference between the output signal and the input signal is equal to the phase shift amount of the phase shifter 10, and the phase shift amount of the phase shifter 10 changes depending on the frequency. By changing it, the oscillation frequency can be changed.

However, with such a conventional configuration, the phase shifter 5 is disposed inside the integrated circuit due to limitations on the number of terminals of the integrated circuit, etc., and therefore it is not possible to obtain a phase shifter with good temperature characteristics. That is, when a capacitor is formed with an integrated circuit, it is particularly susceptible to temperature effects.

Therefore, the output vector E of the phase shifter 5 is the second
As shown in the figure, the output vector F of the adder 8 changes to F' as the temperature changes, and the oscillation frequency changes as a result. It had the disadvantage of poor stability.

Therefore, the present invention has been devised in view of these points, and an object of the present invention is to provide a voltage controlled oscillator whose oscillation frequency is stable against changes in the temperature of an integrated circuit.

In order to achieve the above object, the present invention provides another voltage control amplifier between the phase shifter and the adder inside the integrated circuit, and further controls this voltage control amplifier by the output voltage of the temperature detector to form the adder. By adjusting the voltage applied to the adder, the phase change of the waveforms added by the adder is eliminated, and temperature compensation is achieved.

Next, the present invention will be explained using the drawings.
FIG. 3 is a block diagram showing the configuration of an embodiment of the present invention, and FIG. 4 is a vector diagram of signals at each point A to G in FIG. In FIG. 3, the same parts as in FIG. 1 are denoted by the same reference numerals, and their explanation will be omitted.

Both the voltage controlled amplifier 11 and the temperature detector 12 are arranged inside the integrated circuit 1' . The oscillation operation is similar to the conventional example.

First, when the internal temperature of the integrated circuit changes, the output vector of the phase shifter 5 changes from E to E' in Figure 4, but at this time the output voltage changes depending on the temperature. A voltage control amplifier 11 is controlled by the output of the detector 12.
Therefore, by increasing the amplification degree of the voltage control amplifier 11 and increasing the magnitude of the vector G, the output vector F of the adder 8 changes in magnitude as shown in F', but the phase remains unchanged. Can be controlled. Therefore, even if the temperature changes, the phase angles of E and A can be prevented from changing, so that the oscillation frequency also does not change with respect to temperature changes, and a voltage controlled oscillator with good temperature stability can be obtained.

FIG. 5 is a circuit diagram showing an embodiment of FIG. 3. The inverting amplifier 3 is composed of transistors 21, 24, constant current sources 22, 25, and resistors 23, 26, 27. Further, the phase inverter 4 includes transistors 27 and 29, constant current sources 28 and 35, and a resistor 30. Phase shifter 5 includes transistors 31,3
3. Consists of constant current sources 32, 35, resistors 34, 46, and capacitor 47. The voltage control amplifier 6 includes transistors 36 and 38, a constant current source 40, and resistors 37, 39, and 41. Voltage control amplifier 11, temperature detector 12, adder 8 includes transistors 42, 49, 53, diode 43, constant current sources 44, 51, 54, resistors 45, 48, 5
The diode 43 functions as a temperature detection element, and the collector of the transistor 42 is added as an adder. The phase shifter 10 outside the integrated circuit is composed of a resistor 55 and a capacitor 56.

Next, the operation of the temperature detector shown in FIG. 5 will be explained using an equivalent circuit shown in FIG. 6.
Transistors 61, 65, constant current sources 62, 63,
66, a diode 64, and resistors 67 and 68, the following equation holds true.

V _B61 = V _C −V _D V _B65 = V _C −I・R ₆₇ V _D ≒kT/qlnI/Is {V _B61 , V _B65 : Base voltage of transistors 61 and 65, V _C : Power supply voltage, V _D : Forward voltage drop of diode 64, I: current flowing through constant current sources 63 and 66, k: Boltzmann constant, T: absolute temperature, q:
Electron charge, Is: Transistor saturation current} Therefore, V _B61 changes depending on the temperature. At room temperature,
If designed so that V _D = I・R ₆₇ , the transistors 61 and 65 will be balanced at room temperature, and as the temperature changes, the balanced state of the transistors 61 and 65 will shift and an output voltage will be output depending on the temperature. It turns out.

As explained above, in the present invention, a temperature detector and a voltage control amplifier are provided inside the integrated circuit to control the output voltage of the phase shifter inside the integrated circuit, thereby eliminating phase shift due to temperature changes. , which has the effect of reducing the temperature drift of the output oscillation frequency.

For example, the temperature characteristic of a conventional 2.5 MHz voltage controlled oscillator was 40 KHz/°C, but with the method of the present invention, it can be reduced to within 10 KHz/°C.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a conventional voltage controlled oscillator, FIG. 2 is a vector diagram at each point in FIG. 1, FIG. 3 is a block diagram showing the configuration of an embodiment of the present invention, and FIG. 4 is a vector diagram at each point in FIG. 3, FIG. 5 is a circuit diagram showing an embodiment of FIG. 4,
FIG. 6 is a circuit diagram of the temperature detector. 2... Input terminal, 3... Inverting amplifier, 4... Phase inverter, 5... Phase shifter, 6... Voltage control amplifier, 7... Voltage control input terminal, 8... Adder, 9
... Output terminal, 10 ... Phase shifter, 11 ... Voltage control amplifier, 12 ... Temperature detector.

Claims (1)

[Claims] 1 Inside the integrated circuit, an inverting amplifier, a phase inverter,
A first phase shifter, a first voltage controlled amplifier, and an adder are provided, the output of the inverting amplifier is input to the phase inverter and the first phase shifter, and the output of the phase inverter is input to the the output of the first voltage controlled amplifier is input to the adder, the output of the first phase shifter is input to the adder, and the output of the adder is input to the adder; the output of the second phase shifter is input to an inverting amplifier inside the integrated circuit;
In a voltage controlled oscillator whose oscillation frequency is changed by a voltage controlled amplifier, a second voltage controlled amplifier is provided between the output of the first phase shifter and the input of the adder inside the integrated circuit, Furthermore, a temperature detector is provided that outputs a voltage depending on the temperature inside the integrated circuit, and the output of this temperature detector is added to a second voltage control amplifier to control the second voltage control amplifier. Features of voltage controlled oscillator.