JP3441628B2 - Amplitude detection circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amplitude detection circuit, and more particularly to a technique for improving the temperature characteristic of a detection signal.

[0002]

2. Description of the Related Art In a receiver or the like, an amplitude detection circuit for outputting a current corresponding to the strength of an input signal may be added to an amplification circuit for amplifying the input signal. As an example of this amplitude detection circuit, there is a circuit disclosed in Japanese Patent Publication No. 25733/1992.

The circuit disclosed in this publication, as shown in FIG. 5, has differential amplifiers 100, 10 connected in cascade.
2 and the amplitude detection circuit 104. Then, the amplitude detection circuit 104 includes the differential amplifiers 100, 10
Including circuit means 110, 112 for generating an amount of current corresponding to the potential of the two common emitters 106, 108,
The current generated in each circuit means 110, 112 is applied to the node 1
It is collected at 14 and its sum is available at output 116.

In this way, each differential amplifier 100, 102
Since the potentials of the common emitters 106 and 108 of the input and output rise and fall according to the strength of the input signal input from the input 118, the output 116 of the amplitude detection circuit 104 has a current corresponding to the strength of the input signal, more specifically, the input. It is possible to obtain a current that is a linear function of the logarithm of the signal.

[0005]

However, since the differential amplifiers 100 and 102 of the above circuit have a temperature characteristic of voltage gain in a proportional operation state and a temperature characteristic of saturation amplitude in a saturated operation state, the amplitude detection circuit. There is a problem that those temperature characteristics appear in the output 116 of 104.

In this respect, first, the differential amplifiers 100 and 102
It is conceivable that a predetermined potential generated so as to cancel the temperature characteristic of the saturation amplitude is applied to the bias 120 to drive the power supply transistors 122 and 124. But,
With this configuration alone, the contribution of the temperature characteristics of the voltage gains of the differential amplifiers 100 and 102, which is approximately inversely proportional to the absolute temperature, still remains in the common emitters 106 and 108, and these contributions to the output of the amplitude detection circuit 104. The problem remains that the temperature characteristics are reflected.

On the other hand, it is possible to cancel the temperature characteristic of the voltage gain by multiplying the potentials appearing at the common emitters 106 and 108 of the differential amplifiers 100 and 102 by a potential almost proportional to the absolute temperature. However, for this purpose, it is necessary to prepare an ideal analog multiplier having no temperature characteristic, which causes a problem that the circuit size of the amplitude detection circuit 104 is increased.

The present invention has been made in view of the above problems, and an object thereof is to provide an amplitude detection circuit capable of improving temperature characteristics without significantly increasing the circuit scale.

[0009]

[0010]

In order to solve the above problems, the present invention includes a current generating circuit for generating a current corresponding to a potential appearing at a common node of a differential amplifier for amplifying an input signal. In an amplitude detection circuit that detects the amplitude of an input signal based on a current generated by a current generation circuit, the current generation circuit includes a transistor whose collector current is the current, and the emitter of the transistor has a resistor. The common node of the differential amplifier is connected via the, and the base is supplied with a potential created by using a current that increases substantially in proportion to the absolute temperature.

According to the present invention, the input signal is amplified by the differential amplifier, and a rectified signal corresponding to the amplitude of the input signal appears at the common node thereof. Then, the current generating circuit generates a current corresponding to the potential of this common node. The amplitude detection circuit according to the present invention detects the amplitude of the input signal based on this current.

Here, the current generating circuit includes a transistor. The common node is connected to the emitter of the transistor via a resistor, and the absolute temperature proportional potential is applied to the base. Therefore, a current corresponding to the potential appearing at the common node of the differential amplifier flows in the collector.

At this time, the common node of the differential amplifier may include the temperature characteristic of voltage gain as described above. The temperature characteristic of this voltage gain includes at least a contribution that is almost inversely proportional to the absolute temperature, and has a negative temperature characteristic. In the present invention, a potential (having a positive temperature characteristic) created by using a current that increases substantially in proportion to the absolute temperature, at the base of the transistor of the current generation circuit.
It is possible to cancel them approximately by adding, and it is possible to easily improve the temperature characteristic of the potential difference between the base and the emitter in the temperature range practically required.

The current that increases substantially in proportion to the absolute temperature is a current that can be easily obtained from a conventionally widely used bandgap power supply circuit. In addition, the electric potential generated by using this current has a positive temperature characteristic because it includes a contribution that increases almost in proportion to the absolute temperature.

As a result of the above, according to the present invention, the temperature characteristic of the collector current flowing corresponding to the potential difference between the base and emitter can be improved, and an amplitude detection circuit having a good temperature characteristic can be realized. it can. Further, as described above, the current that increases substantially in proportion to the absolute temperature can be easily taken out from the bandgap circuit widely used as the power supply circuit of the IC using the silicon process. The temperature characteristic of the amplitude detection circuit can be improved without increasing the circuit scale.

[0016]

Further, the present invention is provided corresponding to at least some of the differential amplifiers connected in cascade for amplifying the input signal, and corresponds to the potential appearing at the common node thereof. In an amplitude detection circuit that detects the amplitude of the input signal by converting the current corresponding to the total amount of the currents generated by these current generation circuits into a voltage, The current generating circuit includes a transistor whose collector current is a current corresponding to a potential appearing at the common node of the differential amplifier, and the emitter of the transistor is connected to the common node of the differential amplifier via a resistor. It is characterized in that it is connected and that the base is given a potential created by means of a current which increases approximately in proportion to the absolute temperature.

In the present invention, the input signal is amplified by the plurality of differential amplifiers connected in cascade. At least some of the plurality of differential amplifiers are provided with the current generating circuits corresponding thereto, and they correspond to the potential appearing at the common node of the corresponding differential amplifiers. To generate the respective currents. The current corresponding to the total amount of this current has a predetermined relationship with the amplitude of the input signal, and is the RSSI (Receiv
ed Signal Strength Indicator) Current is well known. In the present invention, in particular, in these current generating circuits, the potential of the common node of each differential amplifier is received by the emitter of the transistor through the resistor, and the base uses a current that increases substantially in proportion to the absolute temperature. Is given the electric potential created. This makes it possible to realize the RSSI function having good temperature characteristics in the amplitude detection circuit.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION As an embodiment of the present invention, an example in which an amplitude detection circuit is added to a circuit in which a plurality of differential amplifiers for amplifying an input signal are connected in cascade will be described.

FIG. 1 is a schematic diagram showing a part of an amplification circuit with an amplitude detection circuit according to this embodiment, and FIG. 2 is a diagram showing a power supply circuit for driving this circuit.

In the following, first, the amplification circuit with the amplitude detection circuit will be described. As shown in FIG. 1, this circuit 1 includes differential amplifiers 2 and 3 corresponding to the last two stages of a large number of cascaded differential amplifiers. Differential amplifier 2
Is configured to include transistors Q1 and Q2,
The differential amplifier 3 is configured to include transistors Q3 and Q4. Then, the inverted outputs of the differential amplifier of the preceding stage (not shown) are respectively input to the bases of the transistors Q1 and Q2 of the differential amplifier 2, and the outputs 4 and 5 thereof are respectively passed through the transistors Q5 and Q6 (emitter follower) and the difference of the latter stage. It is adapted to be inputted to the bases of the transistors Q3 and Q4 of the dynamic amplifier 3, respectively. In order to match the operating characteristics of the differential amplifiers 2 and 3, in the differential amplifier 3, the outputs 6 and 7 of the transistors Q3 and Q4 are connected to the bases of the transistors Q7 and Q8, respectively, and the collectors of these transistors Q7 and Q8 are connected. together are connected to operating potential V _CC, an emitter transistor Q9,
It is grounded through Q10 and resistors R1 and R2, respectively.

Further, the differential amplifier 2 includes a transistor Q
The emitters of 1 and Q2 are each connected to a common node 8. On the other hand, the collectors of the transistors Q1 and Q2 are connected to the operating potential V _CC via load resistors R3 and R4, respectively. Similarly, in the differential amplifier 3, the emitters of the transistors Q3 and Q4 are connected to the common node 9, and the collectors of the transistors Q3 and Q4 are connected to the operating potential V _CC through the load resistors R5 and R6, respectively.

In the differential amplifier 3, the common node 9 is connected to the collector of the power supply transistor Q11. The power transistor Q11 has an emitter connected to the resistor R7.
It is grounded through and the bias potential V _REF supplied from the power supply circuit shown in FIG. 2 is applied to the base. Although such a configuration is not shown, the differential amplifier 2 is similarly provided.

The circuit 1 shown in FIG.
It includes a current generation circuit 10 for generating a current corresponding to the potential appearing at the common node 9 of the. This current generation circuit 10
Is configured to include a detection transistor Q12,
The emitter is connected to the common node 9 of the differential amplifier 3 via the resistor R8, while the base is applied with the reference potential V _R supplied from the power supply circuit shown in FIG. The collector of the detecting transistor Q12 is connected to the current mirror circuit 11 including the transistors Q13 and Q14 and the resistors R9 and R10, and the current corresponding to the current flowing between the collector and the emitter of the detecting transistor Q12 is smoothed by the resistor 11 and the smoothing circuit. It flows through the capacitor C, and the potential applied to the resistor 11 is obtained at the output 12. The amplitude detection circuit for detecting the amplitude of the input signal is configured to include the current generation circuit 10 and the current mirror circuit 11.

Although not particularly shown in the figure, a circuit similar to the current generating circuit 10 can be connected to the differential amplifier 2 as well. In this case, by connecting the collector of the detection transistor included in the added current generation circuit to the collector of the detection transistor 12, the current corresponding to the sum of the currents generated in the current generation circuits is converted into the current mirror circuit. You can run to 11. With this configuration, a so-called RSSI current can be obtained by the current mirror circuit 11.

Next, a power supply circuit for driving the amplification circuit with the amplitude detection circuit described above will be described. As shown in FIG. 2, the power supply circuit 20 first includes a transistor Q2.
1, Q22 and Q23 and resistors R21, R22 and R23
And a current mirror circuit 21 including a transistor Q2
4 and Q25 and resistors R24 and R25, and a current mirror circuit 23 that includes transistors Q26 and Q27 and resistors R26 and R27.
And are equipped with. Further, the power supply circuit 20 includes a bandgap circuit 24 including transistors Q28 and Q29 and resistors R28 and 29, and the current mirror circuit 2
1 gives a known equal collector current to the transistors Q28 and Q29, so that the bandgap potential V _BGAP is obtained at their bases (common).

If the size of the transistor Q28 is N times the size of the transistor Q29, the band gap potential V _BGAP has the value shown in the following equation (1).

[0028]

[Equation 1] Here, V _T is given by the following equation (2).

[0029]

[Equation 2] However, K is the Boltzmann constant, and q is the charge amount of electrons.

First, in the above equation (1), V _BE is the base-emitter voltage of the transistor Q29, and the first term has a negative temperature characteristic. On the other hand, since V _T has a positive temperature characteristic as is clear from the above equation (2), the second term of the above equation (2) has a positive temperature characteristic. Therefore, resistors R28 and R
If the ratio of 29 is optimized, this bandgap potential V
_BGAP has a voltage that does not depend on temperature. The bandgap potential V _BGAP has a value approximately equal to the bandgap voltage of silicon (about 1.2 V), as is well known to those skilled in the art.

Further, as described above, the band gap circuit 2
The size of transistor Q28 of 4 is transistor Q29
Is N times the size of the current mirror circuit 2
The current I flowing through the resistor R25 and the transistor Q25 at 2
_REF (hereinafter referred to as "absolute temperature proportional current") has a value shown in the following equation (3).

[0032]

[Equation 3] The voltage proportional to the absolute temperature I _REF is dropped by the resistor 30, and its potential is passed through the transistor Q30.
Reference potential V _R shown in the following equation (4) is adapted to obtain at the output 25.

[0033]

[Equation 4] However, α is given by the following equation (5).

[0034]

[Equation 5] Here, the second term V _BE of the equation (4) is the transistor Q30.
Is due to the voltage between the base and the emitter of the circuit 1, and is for canceling the voltage drop in the transistors (emitter followers) Q5, Q6, etc. connected between the differential amplifiers 2, 3 of the circuit 1. That is, by setting the bias current of the transistor Q30 to the same value as the bias current of the transistors Q5, Q6, etc., it is possible to cancel the voltage drop between the base and emitter of the transistors.

The potential obtained at the collector of the transistor Q22 is given to the base of the transistor Q31,
Transistor Q whose emitter is grounded via resistor 31
32 and the transistor Q26 are driven. The bandgap potential V _BGAP obtained at the bases of the transistors Q28 and Q29 is
The bias potential V _REF shown in the following equation (6) is obtained from the output 26 via the resistors 32 and Q26 and the resistor 32.

[0036]

[Equation 6] However, V _BE is the base-emitter voltage of the transistor Q26.

The bias potential V _REF thus obtained is
Power supply transistors Q9, Q10, Q11 of the circuit 1 described above
Etc. Then, the emitter current I _E of the power supply transistor is expressed by the following equation (7).

[0038]

[Equation 7] If the signal S (t) is input to the differential amplifiers 2 and 3 and the voltage gain per one stage of the differential amplifier is G, the potential V _E (t) (appearing at the common node 9 of the differential amplifier 3 Hereinafter, "common emitter potential") is expressed by the following equation (8).

[0039]

[Equation 8] In the above formula (8), when the transistors Q5, Q6 and the like (emitter follower) are not used, 2V _{BE of} the third term is simply V _BE .

On the other hand, the reference potential V obtained by the power supply circuit 20.
_R is a transistor Q12 included in the current generation circuit 10.
Given to the base of. On the other hand, since the emitter of the transistor Q12 is connected to the common emitter 9 of the differential amplifier 3 via the resistor R8, the current I _RSSI flowing through the resistor 8 is given by the following equation (9).

[0041]

[Equation 9] Here, the voltage gain G per stage of the differential amplifier is expressed by the following equation (1
0).

[0042]

[Equation 10] The current I _RSSI given by the above equation (9) is passed through the resistor 11 by the current mirror circuit 11. Here, if the carrier wave component is removed by using a low-pass filter, the amplitude detection voltage V _RSSI obtained at the output 12 is given by the following expression (11).

[0043]

[Equation 11] However, a (t) is the envelope of s (t).

As can be seen from the above equation (11), the first term in the parentheses has no temperature characteristic. On the other hand, the third term, which varies according to the envelope of the input signal, has a negative temperature characteristic because it has V _T in the denominator. The second term having a positive temperature characteristic compensates for this. That is, according to the present circuit 1, the coefficient α of the compensation term (second term) is set to an optimum value, so that V _T is caused in a necessary range approximately equal to the guaranteed operation temperature range of the circuit. It is possible to cancel the temperature characteristic that occurs.

[0045]

EXAMPLE An example in which the present invention is applied to an IC limiter amplifier using a silicon process will be described below.

FIG. 3 shows a block diagram of a circuit according to this embodiment. In the figure, differential amplifiers 40a-40f
Has a configuration similar to that of the differential amplifiers 2 and 3 shown in FIG. 1, and they are cascade-connected in six stages. Also,
The power supply circuit 20 has the same configuration as that shown in FIG. Further, the detection circuits 10a to 10e have substantially the same configuration as the current generation circuit 10 shown in FIG.

The differential amplifiers 40a to 40f are connected via an emitter follower (not shown). Since the RSSI function (amplitude detection function) is added to these differential amplifiers, the above-mentioned detection circuit 10a similar to the amplitude detection circuit according to the present invention is used in the second to sixth stage differential amplifiers 40b to 40f. 5 to 10e are connected. The collectors of the transistors included in these five stages of detection circuits are all connected to a common current mirror circuit (not shown), and the sum of the currents generated by them is the so-called RSSI.
I am trying to make it a current. Differential amplifier 40a-40f
The emitter current is about 350 μA, whereas the collector current of the detection transistors included in the detection circuits 10a to 10e is about 4 μA when there is no signal, and this value decreases as the input signal power increases.

FIG. 4 is a diagram showing the RSSI input / output characteristic of this circuit. RSSI output characteristics shown in the figure, using a sine wave of 242MH _Z as an input signal, 0 ° C. to ambient temperature IC, it is measured instead of the three types of 25 ° C., 70 ° C..

As can be seen from the figure, according to the present invention, the temperature characteristics of the amplitude detection circuit can be improved to such an extent that there is no practical problem.

[Brief description of drawings]

FIG. 1 is a diagram showing a circuit including an amplitude detection circuit according to an embodiment of the present invention.

FIG. 2 is a diagram showing a power supply circuit for driving the circuit shown in FIG.

FIG. 3 is a diagram showing a block diagram of a circuit used in an embodiment of the present invention.

FIG. 4 is a diagram illustrating how the temperature characteristics are improved.

FIG. 5 is a diagram showing a conventional amplitude detection circuit.

[Explanation of symbols]

2, 3 differential amplifier, 9 common node, 10 current generation circuit, Q12 (for detection) transistor, R8 resistor,
V _R reference potential.

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Claims (2)

(57) [Claims] 1. A current generating circuit that generates a current corresponding to a potential appearing at a common node of a differential amplifier that amplifies an input signal, and detects the amplitude of the input signal based on the current generated by the current generating circuit. In the amplitude detection circuit, the current generation circuit includes a transistor having the current as a collector current, the emitter of the transistor is connected to the common node of the differential amplifier via a resistor, and the base is connected to the base. An amplitude detection circuit characterized by being supplied with a potential created by using a current that increases substantially in proportion to an absolute temperature. 2. A current amplifier, which is provided corresponding to at least a part of a plurality of differential amplifiers connected in cascade for amplifying an input signal, and which has a potential appearing at a common node thereof. An amplitude detection circuit including a plurality of current generating circuits for generating, wherein the current corresponding to the total amount of the currents generated by these current generating circuits is converted into a voltage to detect the amplitude of the input signal. Comprises a transistor whose collector current is a current corresponding to the potential appearing at the common node of the differential amplifier, the emitter of the transistor being connected to the common node of the differential amplifier via a resistor, and the base An amplitude detection circuit characterized in that an electric potential created by using a current that increases substantially in proportion to the absolute temperature is applied to.