JPH0471363B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention improves the temperature compensation means of MOSFET used for push-pull amplification, etc.
Regarding MOSFET amplifiers.

[Conventional technology]

A conventional temperature compensated push-pull amplifier is constructed as shown in FIGS. 1 and 2. FIG. 1 is a schematic diagram showing the entire configuration of an amplifier, and FIG. 2 is a circuit configuration diagram embodying FIG. 1. That is, this push-pull amplifier includes an amplifier circuit 1 using silicon-based bipolar transistors 1a, 1a, and the bipolar transistors 1a, 1a installed therein.
A radiator 2 for dissipating heat generated from the transistors 1a, 1a, a temperature sensor 3 for detecting the temperature of the radiator 2 and the surroundings and outputting an electric signal in accordance with the temperature, and a bias circuit 4. It is configured.

More specifically, in FIG. 2, the amplifier circuit 1 includes the bipolar transistors 1a, 1a interposed between the input transformer 1b and the output transformer 1c, which generate a phase-inverted component signal from the signal Sin. The signal output from the input transformer 1b is amplified by the bipolar transistors 1a, 1a and given to the output transformer 1c, and the midpoint of the primary winding of the output transformer 1c is connected to the power supply. Vcc provides an idle current Iid for eliminating output waveform distortion of the bipolar transistors 1a, 1a.
Next, a diode 3a is used as the temperature sensor 3, and its cathode side is grounded, and its anode side is connected to the input sides of bipolar transistors 1a, 1a via a coil 1d. This diode 3a is made of silicon and has almost the same characteristics as the bipolar transistor 1a. In the figure, +V is a bias power supply and V _B is a bias voltage.

Thus, the bipolar transistor 1a used in the amplifier circuit 1 exhibits a V _BE -I _C characteristic as shown in FIG. 3 with respect to temperature changes. In other words, the temperature characteristics of V _BE of silicon-based transistors are approximately -2mV/
Varies at a rate of °C. Expressing this using a formula, if the base-emitter voltage V _BE of the transistor 1a at room temperature Tnor is V ₁ and the temperature changes by ΔT (°C) in this state, then
The voltage V _BE is V _BE = V ₁ + (-2 [mV]) x ΔT (1).

Therefore, even if the bias voltage is set to V _B = V ₁ , if a temperature compensation means is provided,
The idle current at Tnor changes to Iid1, that at high temperature Th changes to Iid2, and that at low temperature Tl changes to Iid3. Therefore, at high temperature Th, Iid2>Iid1 and the power gain of bipolar transistor 1a becomes large.
On the other hand, when the temperature is low Tl, Iid3<Iid1, and the power gain of the bipolar transistor 1a becomes small, and the output of the amplifier circuit 1 changes due to temperature changes, making it impossible to obtain favorable results. Therefore, in order to keep the power gain almost constant, the relationship Iid1=Iid2=Iid3...(2) must hold. In other words, since the silicon-based bipolar transistor 1a exhibits the characteristics shown in Figure 3, when changing from room temperature Tnor to high temperature Th or low temperature Tl, if it is translated in parallel,
The relationship in equation (2) is satisfied, and the collector current at the time of output is constant.

As a temperature compensation means for this parallel movement, a silicon diode 3a (temperature coefficient of about -2 mV/°C) having almost the same characteristics as the bipolar transistor 1a is used as the temperature sensor 3 to detect temperature changes, and at high temperature Th, V ₁ → By changing the bias voltage V _B such that V ₁ →V ₃ at low temperature Tl and biasing the bipolar transistors 1a _and 1a, temperature compensation is performed so that the power gain is constant. . Note that, conventionally, a heat-sensitive resistor is used in place of the diode 3a.

By the way, in recent years, push-pull amplifiers etc.
MOSFETs are becoming increasingly popular. Figure 4 is a diagram showing its specific configuration, where 1e is an enhancement type MOSFET.
It shows. Although the device using this MOSFETIe uses a heat sink 2 to dissipate heat, it does not include temperature compensation means as shown in FIG. The reason for this is that the V _GS -I _D characteristic of the enhancement type MOSFET 1e does not change with a constant temperature coefficient with respect to temperature changes, as is clear from Figure 5, that is, the temperature coefficient differs at the bias point, and This is because the temperature compensation means of the bipolar transistor _1a cannot be applied as is because it exhibits negative and positive characteristics with respect to changes in either the high temperature Th or the low temperature Tl with respect to the intersection voltage VO. Specifically, if the gate-source voltage V _GS of MOSFET 1e changes by ΔV _GS , it exhibits negative characteristics when ΔV _GS <V _O ,
When V _GS > _VO , it exhibits positive characteristics. This is due to the fact that the temperature coefficient is not constant like in silicon-based transistors, so even if the bias voltage V _B is temperature compensated to keep the idle current constant as described above, a parallel shift relationship holds. Therefore, the temperature characteristics of the drain current during output cannot be covered.

In general, if the temperature is constant in the slope region, increasing the idle current will reduce the transconductance.
gm increases and power gain increases. Therefore, by increasing the idle current as the temperature rises, gm increases and the output can be kept constant. but,
Unlike silicon-based transistors, there are no fixed rules, so if the bias voltage V _{B changes with the intersection voltage V O} as the _boundary , the above idea becomes difficult to apply, and it also applies over a wide range from low temperatures to high temperatures, with room temperature in between. There is a problem that temperature compensation cannot be performed.

Therefore, a temperature compensator for a circuit using an element such as a thermistor or a varistor whose temperature characteristics are non-linear has been proposed (Japanese Patent Publication No. 36141/1983).

A case where this temperature compensator is applied to a MOSFET amplifier will be explained using FIGS. 6 and 7.

That is, it is assumed that 11 in FIG. 6 is a push-pull amplifier circuit using, for example, enhancement type MOSFETs 11a and 11a, and is configured as shown in FIG. 4, for example. 12 is
It is a heat radiator to which the MOSFETs 11a, 11a and other functional elements are attached, and which radiates heat generated by these functional elements. 13 is MOSFET1
This is a temperature sensor that is attached to the case of 1a or the heat sink 12, etc., and detects the temperature of the MOSFET 11a or the surroundings including the MOSFET 11a, and generates an electric signal in response to the detected temperature. Connected to the output end of the temperature sensor 13 is a circuit 14 that converts the temperature coefficient in response to temperature changes and controls the bias voltage to a required value. 15 is a signal
This is an input signal detection circuit that detects the rising edge of Sin and supplies power to the circuit 14 that controls the bias.

Next, a more specific detailed circuit will be explained with reference to FIG. This amplifier has a configuration that is particularly effective only for long-term temperature compensation that does not take into account the rise of the input signal Sin. Specifically, temperature sensor 1
3 is, for example, a silicon diode 13a.
is used, and is attached to the heat sink 12, for example. This diode 13a is, for example, −
Heatsink 1 with a temperature coefficient of 2mV/℃
2 and the surrounding temperature are detected and a voltage V corresponding to the detected temperature is output. The circuit 14 for controlling the bias includes resistors R1, R
a temperature coefficient conversion circuit 14A that includes a voltage divider circuit of 2 resistors and that changes the temperature coefficient of the temperature sensor 13 in response to the voltage V; and a bias power supply that outputs a bias adjustment signal V _REF for adjusting the operating bias voltage of the MOSFET 11a. 14B, an operational amplifier OP, and a resistive voltage divider circuit of resistors R1 and R2, receives the output of the temperature coefficient conversion circuit 14A and the bias adjustment signal V _REF , and outputs the required bias voltage V _B to be applied to the MOSFET 11a. The bias control circuit 14c is configured with a bias control circuit 14c.
The output terminal of c is connected between both coils 1d and 1d (V _B ) shown in FIG.

Next, the operation of the amplifier configured as above will be explained.

When designing, first, the idle current Iid
, and then determine the corresponding temperature coefficient. The heat generated by the operation of MOSFET11a is
The heat is transmitted to the heat sink 12 through the FET case, and the temperature of the heat sink 12 changes while being influenced by the ambient temperature. The temperature of this radiator 12 is detected by a temperature sensor 13, for example, a silicon diode 13a, and after being converted into a voltage V with a temperature coefficient of -2 mV/°C, it is introduced into this temperature coefficient conversion circuit 14A. be done. Here, conversion circuit 1
4A is applied to the inverting input terminal of the operational amplifier OP by dividing the voltage V by resistors R1 and R2. On the other hand, a bias adjustment signal V _REF is input from the bias power supply 14B to the non-inverting input terminal of the operational amplifier OP. Therefore, the bias control circuit 14c outputs a bias voltage as follows: V _B =(1+R2/R1)V _REF -R2/R1V (3). Here, temperature T
Since the output voltage V of the temperature _sensor 13 changes due to a change in When used, ∂V/∂T=-2 [mV/℃] ...(5), so if we look specifically at the temperature dependence of voltage V in equation (3), ∂V/∂T= 2・R2/R1 [mV/℃] ...(6) Therefore, by varying the resistance R1,
An arbitrary temperature coefficient ∂V _B /∂T is obtained. Then, as shown in FIG. 5, the resistor R1 is adjusted manually, for example, so that this temperature coefficient becomes the temperature coefficient at the bias point of the designed value. After the temperature coefficient is determined in this way, by varying the bias adjustment signal V _REF based on equation (3), the MOSFET 11
The bias voltage V _B to be applied to a is determined to be the required value, and the idle current Iid is adjusted to the designed value.

[Problem to be solved by the invention]

However, as shown in Figures 6 and 7
MOSFET amplifiers also have the following problems that must be solved.

In other words, in order to eliminate power loss in the MOSFET 11a during idle, no bias is applied when there is no signal, and when the signal Sin is input, the input signal detection circuit 15 detects the rising edge of the signal Sin and supplies power to the operational amplifier OP. Add V _D and operate
A bias may be applied to the MOSFET 11a. In this case, the temperature of the MOSFET 11a increases, but since the temperature sensor 13 is attached to the radiator 12, a time delay occurs. For this reason,
MOSFET 11a's gm decreases as the temperature rises, and the gain decreases accordingly, so even if a signal Sin with a constant amplitude is input as shown in Figure 8A,
By reducing the gain of MOSFET11a, the MOSFET
From the output of 11a, a signal Sout as shown in Fig. 8B is generated.
will be output.

The present invention was made in view of these circumstances, and by varying the operating bias voltage of the MOSFET with a time constant circuit, for example,
Even if the MOSFET and temperature sensor are installed far apart, the power gain of the amplifier circuit can be controlled to a predetermined value in a short time even when the MOSFET and temperature sensor are installed, and the MOSFET has an excellent temperature compensation function against temperature changes.
The purpose is to provide an amplifier.

[Means to solve the problem]

In order to solve the above problems, the present invention
a temperature sensor that is attached to a MOSFET or a heat sink that dissipates heat generated by the operation of the MOSFET and outputs an electrical signal corresponding to the temperature;
A bias power supply that outputs a bias adjustment signal to adjust the operating bias voltage of the MOSFET, a temperature coefficient conversion circuit that receives an electrical signal from the temperature sensor and converts the temperature coefficient of the temperature sensor, and a temperature coefficient conversion circuit that converts the temperature coefficient of the temperature sensor. A MOSFET amplifier consisting of a bias control circuit that receives the output signal and bias adjustment signal and outputs the required bias voltage to be applied to the MOSFET, and an input signal detection circuit that detects the input signal and supplies power to the bias control circuit. The temperature coefficient conversion circuit and the bias control circuit include an operational amplifier, a resistive voltage divider circuit on the inverting input terminal side and the output terminal side of the operational amplifier, and a capacitor connected to a part of the resistor of the resistive voltage divider circuit. a time constant circuit which divides the output from the temperature sensor with a time constant and supplies it to the inverting input terminal; and a bias adjustment signal from a bias power supply supplied to the non-inverting input terminal of the operational amplifier. It has a circuit that outputs an operating bias variable according to the time constant of the time constant circuit.

[Effect]

First, it has been found that the cause of the output of the signal Sout shown in FIG. 8B is caused by the time delay T1 between the MOSFET channel cases and the time delay T2 from this case to the temperature sensor 13. Therefore, by compensating for the time delays of T1 and T2, temperature compensation of the MOSFET can be performed almost simultaneously with signal input. In this case, if the bias voltage V _B is lowered, gm will decrease and the gain will decrease accordingly, so if the bias voltage is varied and applied to MOSFET 11a as shown in Figure 9, the problem caused by the time delay will be solved. be able to.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 10 is a circuit diagram showing the temperature coefficient conversion circuit and bias control circuit of the MOSFET amplifier of the embodiment. In addition, the heat sink 12 and
The push-pull amplifier circuit 11 using the MOSFET 11a has the same configuration as in FIGS. 6 and 7, and therefore the explanation thereof will be omitted.

That is, this circuit is a circuit realized based on the above-mentioned theory, and includes an input signal detection circuit 15 that detects the rising edge of the signal Sin, supplies power V _D to the operational amplifier OP, and turns on the operational amplifier OP. For example, the resistor R2 shown in FIG.
Divided into two resistors R21, R22, R23, capacitor C1 and resistor R2 between both resistors R22, R23.
A bias control circuit 14C is provided in which capacitors C2 are connected in parallel between the bias voltage VB and the bias voltage _VB .

Therefore, in the above configuration, generally from the condition T1<<T2, R22・C1<<R2
If a time constant of 3.C2 is chosen, the following equation can be obtained approximately.

V _B1 = (1+R21/R1)V _REF −R21/R1V ……(7) V _B2 ≒(1+R21+R22/R1)V _REF −R21+R22/R1V ……(8) V _B2 ≒(1+R21+R22+R23/R1)V _REF −R21+R22+R23 /R1V ...(9) Also, T1 and T2 are each time constant R22・C
1. Since it is related to R23・C2, capacitor C
1, C2 from MOSFET 1a to temperature sensor 1
It is necessary to select and use it appropriately depending on the heat transfer time to 3a. Therefore, each of the resistors R21,
R22, R23 and capacitors C1, C2 constitute a time constant circuit 16.

Note that the present invention is not limited to the above embodiments. For example, by increasing the number of divisions of resistor 2 shown in FIG.
By increasing 3, the rising slope of the bias voltage V _B can be finely corrected. Also, the 12th
As shown in the figure, capacitors C1 and C2 may be individually connected in parallel to each resistor R22 and R23. Furthermore, it goes without saying that any amplifier circuit other than the push-pull amplifier 11 may be used as long as it uses the MOSFET 11a. Further, the temperature sensor 13 is not limited to the diode 13a, and includes all elements with a negative temperature coefficient that generally function as a temperature sensor.

〔Effect of the invention〕

As explained above, according to the MOSFET amplifier of the present invention, the temperature coefficient is varied in response to the output of the temperature sensor, the bias is adjusted to obtain the required bias voltage, and this is applied to the MOSFET, and further, A capacitor or the like is connected to the temperature coefficient conversion circuit so as to have a predetermined time constant. Therefore, even if used in an amplifier circuit
MOSFETs do not have a constant temperature coefficient and
Even if the MOSFET and temperature sensor are installed far apart, temperature compensation can be performed in a short time.
As a result, it is possible to exhibit an excellent temperature compensation function that always maintains the power gain of the amplifier circuit at a constant value against temperature changes.

[Brief explanation of drawings]

Figure 1 is a basic configuration diagram of a conventional amplifier, Figure 2 is a circuit configuration diagram that embodies Figure 1, and Figure 3 shows how the silicon-based bipolar transistor used in the amplifier circuit shown in Figure 2 responds to temperature changes. V _BE −
Characteristic diagram of _I
Characteristic diagram of V _GS - _ID , Figure 6 is a basic configuration diagram of a conventional MOSFET amplifier, Figure 7 is a specific configuration diagram of the conventional amplifier, Figure 8 is an output waveform diagram of the conventional amplifier, and Figure 9 Figures 1 to 10 show embodiments of the present invention.
These are diagrams for explaining MOSFET amplifiers, and Figure 9 is a diagram showing the relationship between time and bias voltage.
FIG. 0 is a circuit configuration diagram embodying a part of the MOSFET amplifier, and FIGS. 11 and 12 are diagrams each showing a modified version of FIG. 10. 11...Amplification circuit, 11a...MOSFET, 1
2...Radiator, 13...Temperature sensor, 14A...
Temperature coefficient conversion circuit, 14B...Bias power supply, 1
4C...Bias control circuit, 15...Input signal detection circuit, 16...Time constant circuit, R1, R21, R
22, R23...Resistor, C1, C2...Capacitor.

Claims (1)

[Claims] 1. A temperature sensor 13a that is attached to the MOSFET 11a or a heat sink 12 that dissipates heat generated by the operation of this MOSFET, and that outputs an electric signal corresponding to the temperature, and that adjusts the operating bias voltage of the MOSFET. a bias power supply 14B that outputs a bias adjustment signal for the temperature; a temperature coefficient conversion circuit 14A that receives an electrical signal from the temperature sensor and converts the temperature coefficient of the temperature sensor; and an output signal from the temperature coefficient conversion circuit. a bias control circuit 14C that receives the bias adjustment signal and outputs a required bias voltage to be applied to the MOSFET;
an input signal detection circuit 15 that detects an input signal and supplies power to the bias control circuit.
In the MOSFET amplifier, the temperature coefficient conversion circuit 14A and the bias control circuit 14C include an operational amplifier OP, and resistor voltage divider circuits R21, R22, on the inverting input terminal side and the output terminal side of this operational amplifier.
R23 and a part of the resistor of this resistance voltage dividing circuit are arranged in parallel with capacitors C1 and C2, and a time constant circuit divides the output from the temperature sensor 13a with a time constant and supplies it to the inverting input terminal. 16, and a circuit that variably outputs the operating bias according to a bias adjustment signal from the bias power supply supplied to the non-inverting input terminal of the operational amplifier and a time constant of the time constant circuit.
MOSFET amplifier.