JP2574706B2 - Transmitter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an automatic level control circuit that automatically controls the gain of an amplifier so as to keep the voltage level of a transmission signal within a predetermined range.

<Conventional technology> Generally, in the communication field, the upper limit of the voltage level of a transmission signal is variously standardized according to the transmission frequency,
Therefore, the transmitter is also provided with an automatic level control circuit (hereinafter, referred to as an ALC circuit) for controlling the voltage level of the transmission signal so as not to exceed the upper limit value.

FIG. 4 shows a conventional example in which an ALC circuit is provided in a transmitter.

In the figure, 1 ₀ ALC circuit 2 ₀ is pre-amplifier capable of gain adjustment, 3 a power amplifier, 4 is an antenna.

Additional ALC circuit 1 _0, in this example, a detection unit 6 for outputting a detection voltage Vin corresponding thereto by detecting the voltage level of the transmission signal, the reference voltage Vref for determining the operating point of the level control of the transmission signal A volume VR ₁ as a reference voltage setting unit for setting, a detection voltage Vin from the detection unit 6 and a reference voltage Vr
a gain controller 8 ₀ for generating a gain control voltage Vout based on the comparison result between ef, consisting ALC amplifier 10 for gain changes according to the magnitude of the gain control voltage Vout.

Gain controller 8 _0, for example, it is an operational amplifier, and a voltage input-output characteristics shown in FIG. 5. That is, when the detected voltage Vin from the detector 6 is smaller than the reference voltage Vref (Vin <Vref) from the gain control unit 8 ₀ is always the gain control voltage Vout of a constant level is output. Therefore, the gain of the ALC amplifier 10 is also constant (for example, G
₀ ) is kept.

On the other hand, when the detection voltage Vin exceeds the reference voltage Vref (Vin ≧
Vref), the gain control unit 8 _0, inverse proportional gain control voltage Vout to the magnitude of the detected voltage Vin is outputted. Therefore, as the detection voltage Vin increases, the gain control voltage Vou
t gradually decreases, and the gain of the ALC amplifier 10 is reduced accordingly.

As a result, as shown in FIG. 6, ALC circuit 1 ₀ voltage level of the transmission signal input reaches a predetermined threshold (e.g.
Exceeds V _1), the transmission signal outputted from the ALC circuit 1 ₀ would the voltage level is limited so as not to exceed the upper limit value (for example, L _1).

As described above <INVENTION An object you try solving>, since the voltage level of the transmission signal has various specifications, to meet these specifications, as shown in FIG. 6, ALC circuit 1 ₀ In some cases, it may be necessary to reset the upper limit of the voltage level of the transmission signal to be limited by L ₁ → L ₂ → L ₃ .

This adjustment is performed by operating the volume VR ₁ to adjust the reference voltage Vref
Is changed by changing the value of L ₁ → L ₂ → L ₃
The voltage level of the transmission signal is
Up to V ₁ , V ₂ , V ₃ , in each case ALC amplifier 10
Whereas the gain is constant (= G _0), the threshold voltage when the voltage level of the transmission signal begins to be regulated by the ALC circuit 1 _0, and so V ₁ → V ₂ → V ₃ Become smaller.

This is because as suppress the upper limit of the ALC circuit 1 ₀ and _{L 1 → L 2 → L 3} , proper input to output characteristics of the transmission signal, i.e. the dynamic range is narrowed and R ₁ → R ₂ → R ₃ Means Accordingly, when the reduced set the upper limit in accordance with the standards (for example set to L ₃₎ is too narrow dynamic range R _3, results in a disadvantage that can not send a valid signal.

The upper limit of the voltage level of the transmission signal to be limited by the ALC circuit 1 ₀ After setting to a predetermined value (e.g. L _3), in order to ensure a dynamic range of some extent wide range, as shown in FIG. 7, ALC front provided on the input side of the circuit 1 ₀ amplifiers 2
₀ adjusted to a gain of the volume VR ₂ be reduced and so G ₀ → G ₁ → G ₂ is one of the measures.

However, if the gain is set too low (for example, G ₂ ),
In earlier stages of the voltage level is limited by the ALC circuit 1 _0, (distortion occurs at greater than or equal _to V ₀ of the voltage of FIG. 7) distortion occurs in the transmission signal, linearity is impaired.

Thus, conventionally, to secure a required dynamic range for the transmission signal, and, to prevent distorted, respectively need to be adjusted individually each volume pre-amplifier 20 and the ALC circuit 1 ₀ And the adjustment operation is complicated.

<Means for Solving the Problems> The present invention has been made in view of such circumstances, and an upper limit value for limiting a voltage level of a transmission signal and a gain for the transmission signal are controlled in cooperation with each other. As described above, that is, when the upper limit value is set, an appropriate gain is uniquely determined in accordance with the upper limit value, and the conventional adjustment operation is further facilitated.

Therefore, the present invention provides a pre-amplifier 2 that amplifies an input transmission signal with a constant gain and outputs the amplified signal, and a detection unit 6 that detects the voltage level of the transmission signal output from the antenna.
And the automatic level control circuit 1 that controls the voltage level of the transmission signal input from the pre-amplifier 2 based on the voltage level detected by the detection unit 6, and is configured as follows.

That is, in the transmitter of the present invention, the automatic level control circuit 1 includes an ALC amplifier 10 that changes a gain for a transmission signal, and a reference voltage setting unit 12 that sets a reference voltage that determines an operation point of voltage level control of the transmission signal. Based on the comparison result between the voltage level of the transmission signal supplied from the detection unit 6 and the reference voltage supplied from the reference voltage setting unit 12, the transmission is performed so as to keep the ALC operating point V _O of the ALC amplifier 10 constant. The gain control unit 8 outputs a gain control voltage that controls the upper limit value and the gain of the signal voltage level in association with each other.

Further, the gain control unit 8 includes an inverting amplifier 16 that generates an output voltage obtained by inverting and amplifying a difference voltage between the detection voltage from the detecting unit 6 and the reference voltage, and an output voltage from the inverting amplifier 16 is a reference voltage. When the output voltage is larger than the reference voltage, the output voltage is held at a constant voltage level corresponding to the magnitude of the reference voltage and is output as a gain control voltage, while the output voltage from the inverting amplifier 16 is higher than the reference voltage. When the output voltage is small, a limiter circuit 18 that outputs the output voltage as it is as a gain control voltage can be provided.

<Operation> In the above configuration, the reference voltage Vref is set by the reference voltage setting unit 12.
Is set, the inverting amplifier 16 generates an output voltage Vx obtained by inverting and amplifying the difference voltage between the detection voltage Vin from the detection unit 6 and the reference voltage Vref.

When the output voltage Vx of the inverting amplifier 16 is higher than the reference voltage Vref (Vx ≧ Vref), the limiter circuit 18 holds the output voltage Vx at a constant voltage level corresponding to the magnitude of the reference voltage, This is output as the gain control voltage Vout.

And the gain control voltage Vout having such characteristics is
Since the signal is supplied to the ALC amplifier 10, the gain of the ALC amplifier 10 is also kept constant. Therefore, the voltage level of the transmission signal is
It is amplified by that gain.

On the other hand, when the output voltage Vx from the inverting amplifier 16 is smaller than the reference voltage Vref (Vx <Vref), the limiter circuit 18 outputs this output voltage Vx as it is as the gain control voltage Vout. Therefore, the gain of the ALC amplifier 10 also decreases, and the voltage level of the transmission signal is maintained at a constant value.

When the reference voltage Vref from the reference voltage generator 12 is changed, the output voltage Vx of the inverting amplifier 16 changes accordingly, and at the same time, the voltage level of the operating point of the limiter circuit 18 also changes. That is, if the reference voltage is changed, the limiter circuit
Since the magnitude of the voltage level that should be kept constant by 18 also changes, the upper limit value of the voltage level of the transmission signal restricted by the ALC circuit 1 also changes.

As described above, the upper limit value and the gain of the voltage level for the transmission signal are controlled in cooperation with each other only by adjusting the reference voltage, so that the adjustment operation of both is facilitated and the required value for the transmission signal is always required. The dynamic range can be ensured, and the voltage level can be limited to an appropriate voltage level that does not exceed the standard value.

<Embodiment> FIG. 1 is a circuit configuration diagram in a case where an ALC circuit is provided in a transmitter, and portions corresponding to those in the conventional example shown in FIG. 4 are denoted by the same reference numerals.

In FIG. 1, 1 is an ALC circuit according to the present invention, 2 is a pre-amplifier set to a constant gain, 3 is a power amplifier,
4 is an antenna.

The ALC circuit 1 detects a voltage level of a transmission signal and outputs a detection voltage Vin corresponding to the voltage level. An ALC operating point V ₀ for level control of the transmission signal (the meaning of this term will be described later). A reference voltage setting unit 12 for setting a reference voltage Vref for determining the
It comprises a gain control unit 8 that generates a gain control voltage Vout based on the result of comparison between n and the reference voltage Vref, and an ALC amplifier 10 whose gain changes according to the magnitude of the gain control voltage Vout.

The gain control section 8 includes an inverting amplifier 16, a limiter circuit 18, and an amplifier 20 in this example.

In this example, the inverting amplifier 16 is connected to the operational amplifier Amp ₁ and each resistor.
R _{1 to} R ₄ . The inverting amplifier 16 receives both the detection voltage Vin from the detection unit 6 and the reference voltage Vref given from the reference voltage setting unit 12, and inputs the detection voltage Vin and the reference voltage Vre.
A voltage Vx obtained by inverting and amplifying the difference voltage from f is output.

Further, in this example, the limiter circuit 18 includes an operational amplifier Amp ₂
And a diode D ₁ and the resistor R ₅ to R _6. The limiter circuit 18 receives both the output voltage Vx from the inverting amplifier 16 and the reference voltage Vref given from the reference voltage setting unit 12, and outputs a signal when the output voltage Vx is higher than the reference voltage Vref (Vx
≧ Vref), the output voltage Vx is output while being held at a constant voltage level corresponding to the magnitude of the reference voltage Vref, while the output voltage Vx from the inverting amplifier 16 is smaller than the reference voltage Vref (Vx <Vref) outputs the output voltage Vx as it is.

In the case of this example, the resistances of the resistors R _{1 to} R _{1 are set} so that the inverting gain of the operational amplifier Amp ₁ forming the inverting amplifier 16 is about twice the inverting gain of the operational amplifier Amp ₂ forming the limiter circuit 18. A value of ₆ is set.

Further, the amplifier 20 converts the output voltage Vx into an ALC amplifier 1
The voltage is adjusted to a voltage level suitable for gain control of 0, and is output to the ALC amplifier 10 as a gain control voltage Vout.

Next, the operation of the ALC circuit 1 having the above configuration will be described with reference to FIG. 2 and FIG.

2, the horizontal axis represents the detection output Vin from the detector 6 and the vertical axis represents the gain control voltage Vout from the ALC circuit 1.
(And the output Vx of the inverting amplifier 16). Also,
In FIG. 3, the horizontal axis represents a transmission signal input to the ALC circuit 1, and the vertical axis represents a transmission signal output from the ALC circuit 1. Therefore, the detection output Vin on the horizontal axis in FIG.
This corresponds to the output of the transmission signal of the transmitter on the vertical axis in FIG.

Now, when transmitting the transmission signal from the antenna 4, the detection unit 6 detects the detection voltage Vin according to the voltage level of the transmission signal.
Is generated, and this detection voltage Vin is applied to the opposite-phase input terminal (−) of the operational amplifier Amp ₁ constituting the inverting amplifier 16 via the resistor R ₁ . To the operational amplifier Amp ₁ of the positive-phase input terminal (+), since the reference voltage Vref is applied from the inverting amplifier 16, the voltage Vx obtained by inverting amplifying a difference voltage between the detection voltage Vin and the reference voltage Vref Is output.

Then, the output voltage Vx of the inverting amplifier 16, together with the applied to the anode of the diode D ₁ of the limiter circuit 18 via the resistor R _3, via a resistor R ₅ reverse phase input terminal of the operational amplifier Amp ₂ - in addition to the () Can be At this time, the reference voltage from the reference voltage setting unit 12 is applied to the positive-phase input terminal (+) of the operational amplifier Amp _2.
Since Vref is applied through the resistor R ₆ to the operational amplifier Amp _2, from the operational amplifier Amp _2, a voltage obtained by inverting amplifying a difference voltage between the output voltage Vx and the reference voltage Vref is output.

Here, when the voltage level of the transmission signal is low, and therefore the output voltage Vx from the inverting amplifier 16 increases and exceeds the reference voltage Vref (Vx ≧ Vref), the operational amplifier Amp _{2 of the} limiter circuit 18 the output of a negative, current flows from the anode side to the cathode side of the diode D _1. Therefore, the level change of the output voltage Vx of the inverting amplifier 16 is suppressed, and the output voltage Vx is maintained at a constant voltage level corresponding to the magnitude of the reference voltage Vref.

Then, the output voltage Vx having the constant level is applied to the ALC amplifier 10 as the gain control voltage Vout via the amplifier 20, so that the gain of the ALC amplifier 10 is constant. As a result, the transmission signal input to the ALC amplifier 10 is amplified with a constant gain.

On the other hand, when the voltage level of the transmission signal is high, and therefore, the output voltage Vx from the inverting amplifier 16 decreases and becomes lower than the reference voltage Vref (Vx <Vref).
Since the output of the operational amplifier Amp ₂ of the limiter circuit 18 becomes positive, the current flowing through the diode D ₁ is cut off.
The output voltage Vx of the inverting amplifier is directly applied to the ALC amplifier 10 via the amplifier 20 as the gain control voltage Vout. As described above, when the output voltage Vx of the inverting amplifier 16 becomes equal to or lower than the reference voltage Vref, the gain control voltage Vout also gradually decreases accordingly, so that the gain of the ALC amplifier 10 also decreases, and the voltage level of the transmission signal decreases. The value is kept constant so as not to exceed the upper limit.

Specifically, in FIG. 2, it is assumed that the reference voltage is set to, for example, Vref ₁ by the reference voltage setting unit 12. At this time, if the operation of the limiter circuit 18 is neglected, the voltage level of the transmission signal is small.
If n still does not exceed the reference voltage Vref ₁ , the inverting amplifier
The output voltage from 16 Vx decreases along one-dot relegation from the position indicated by the symbol a ₁ with an increase in the detection output Vin. However, actually, when the output voltage Vx is higher than the reference voltage Vref ₁ (Vx ≧ Vref ₁ ), the limiter circuit 18 operates to cause a current to flow through the diode D ₁ , and the output voltage Vx from the inverting amplifier 16. Is maintained at a constant level as shown by the solid line in FIG. Thus, since also the gain control voltage Vout is kept constant, the gain G ₁ of the ALC amplifier 10 becomes constant. As a result, as shown in FIG. 3, transmission signal input to the ALC amplifier 10 is amplified with a constant gain G _1.

On the other hand, when the voltage level of the transmission signal increases and the output voltage Vx from the inverting amplifier 16 becomes smaller than the reference voltage Vref ₁ (Vx <Vref ₁ ), the voltage flows through the diode D ₁ of the limiter circuit 18. Since the current is cut off and the operation of the limiter circuit 18 is stopped, the output voltage of the inverting amplifier is
Vx is directly applied to the ALC amplifier 10 via the amplifier 20 as the gain control voltage Vout. Thus, the inverting amplifier 1
Becomes smaller than 6 the output voltage Vx is the reference voltage Vref, the output voltage Vx, in order to decrease along a straight line L ₁ to an extension of the one-dot chain line in FIG. 2, the gain control voltage Vout accordingly
Also gradually declines. As a result, the gain of the ALC amplifier 10 also decreases, the voltage level of the transmission signal, as shown in Figure 3, will be maintained at a constant level of the upper limit value L _1.

As a result, as shown in FIG. 3, since the gain of the ALC amplifier 10 is kept constant, the voltage level of the transmission signal is amplified and output according to the gain,
Since the gain of the C amplifier 10 is reduced, a region where the voltage level of the transmission signal is kept constant appears. Here, it is assumed that the value of the voltage level of the input signal of the ALC circuit 1 corresponding to the inflection point portion that separates the two regions is defined as “ALC operating point V ₀ ”.

Incidentally, description so far, a reference voltage set by the reference voltage setting unit 12 so that for example Vref _1, although a case that secure a constant value, as shown by the solid line of a positive slope in FIG. 2 The reference voltage is changed, for example, from Vref ₁ → Vref ₂ →
By changing it to Vref ₃ , such a reference voltage Vre
The operational amplifier A constituting the inverting amplifier 16 according to the change of f
Since the inverting gain for the detected voltage Vin of mp ₁ becomes gradually smaller, the output voltage Vx becomes smaller accordingly.

For example, when ignoring the effect of the limiter circuit 18, as shown in FIG. 2, (straight line L ₁ which is a start point a ₁₎ →
(Straight line L ₂ was the starting point a ₂₎ → (a ₃ straight line L _3, which was the starting point)
Thus, the gain control voltage Vou with respect to the detection voltage Vin
The output characteristic of t (or the output Vx of the inverting amplifier 16) changes.

However, actually, there is a limiter circuit 18 and, moreover,
Since the reference voltage applied to the operational amplifier Amp ₂ of the limiter circuit 18 is also changed from Vref ₁ → Vref ₂ → Vref ₃ at the same time, the output voltage Vx from the inverting amplifier 16 becomes the respective reference voltages Vref ₁ , Vre
Until reaching f _2, Vref _3, from each of the characteristic curve shown by a one-dot chain line in FIG. 2, (a straight line connecting the Vref ₁ from b ₁₎
→ (straight line connecting b ₂ and Vref ₂ ) → (straight line connecting b ₃ and Vref ₃ )
Is changed. Even in this case, since the level of each output voltage Vx is kept constant without being affected by the change of the detection voltage Vin, the gain of the ALC amplifier 10 becomes G ₁ → G _{2 as} shown in FIG. → will be changed to G _3.

Then, each output voltage Vx is equal to the reference voltage Vref ₁ , Vref ₂ ,
Becomes less than Vref _3, in order to change along a straight line L _1, L _2, L ₃ each in the extension of one-dot chain line, the voltage level of the transmission signal outputted from the ALC circuit 1, in FIG. 3 As shown, the upper limit is changed from L ₁ → L ₂ → L ₃ .

As described above, when the reference voltage Vref is adjusted, the upper limit values L _{1 to} L ₃ of the voltage level for the transmission signal and the gains G _{1 to} G ₃
There in order to be controlled with a coordinated with each other, as a result, ALC operating point V _0, without being affected by the setting of the upper limit value L ₁ ~L _3, always constant.

 The reason will be described.

As described above, the detection voltage Vin of the detection unit 6 corresponds to the transmission signal output of the transmitter,
The detection output Vin on the horizontal axis in the figure corresponds to the output of the transmission signal of the transmitter on the vertical axis in FIG. In consideration of this point, in FIG. ₂ , the voltage levels Vin ₁ and Vi of the detection output of the detection unit 6 corresponding to the respective inflection points indicated by reference numerals Vref ₁ , Vref ₂ and Vref ₃ are shown.
n ₂ and Vin ₃ correspond to the output levels indicated by symbols L ₁ , L ₂ and L ₃ in FIG.

In FIG. 3, the signal input to the ALC circuit 1 is x, the signal y output from the ALC circuit 1 is G, and the gain is G.
When the limiter circuit 18 operates, y = G
X is related. Therefore, in FIG. 3, L ₁ = G ₁ · x ₁ , L ₂ = G ₂ · x ₂ , L ₃ = G ₃ · x ₃ (1). From this, x ₁ = L ₁ / G ₁ , The following relationship is obtained: x ₂ = L ₂ / G ₂ , x ₃ = L ₃ / G ₃ (2)

Further, as described above, the upper limit values L ₁ , L ₂ , and L ₃ are determined by the detection unit 6.
X ₁ = k · Vin ₁ / G ₁ , x ₂ = k · Vin ₂ / G ₂ , x ₃ = k · Vin since they correspond to the detection output voltage levels Vin ₁ , Vin ₂ and Vin ₃ respectively. _{3 of}
G ₃ (3) (where k is a constant of proportionality).

In the present embodiment, as shown in FIG. 2, the gain G ₁ ~G ₃ to the transmission signal, the voltage level Vin ₁ ~ of detector 6
Since Vin ₃ (or the upper limit values L _{1 to} L ₃ ) changes in association with each other, Vin ₁
/ G ₁ = Vin ₂ / G ₂ = Vin ₃ / G ₃ Therefore, x ₁ = x ₂ = x ₃ = V _O (4) That is, the ALC operating point V ₀ is always constant.

As described above, when the reference voltage Vref is adjusted, the upper limit values L _{1 to} L ₃ of the voltage level for the transmission signal and the gains G _{1 to} G ₃
But because they are controlled with a coordinated with one another so as to keep the ALC operating point V ₀ constant both adjustment operation is facilitated.

Moreover, ALC operating point V ₀ which level control of the transmission signal, as shown in FIG. 3, without being affected by the setting of the upper limit value L ₁ ~L _3, always constant, the ALC operation point V _If the voltage of ₀ is set in advance to a level that does not cause signal distortion, a required dynamic range is always secured for the transmission signal, and an appropriate value that does not exceed the standard value without signal distortion is generated. It can be limited to voltage levels.

<Effects of the Invention> According to the present invention, the upper limit value and the gain of the voltage level for the transmission signal are controlled in cooperation with each other only by adjusting the reference voltage. become.

Further, a required dynamic range can always be ensured for a transmission signal, and furthermore, it is possible to limit the voltage level to an appropriate voltage level that does not exceed a standard value without causing signal distortion. The excellent effect of is exhibited.

[Brief description of the drawings]

1 to 3 show an embodiment of the present invention. FIG. 1 is a circuit diagram showing a case where an ALC circuit is provided in a transmitter, and FIG. 2 is a diagram showing a transmission signal when a reference voltage is changed. Detection voltage Vin
FIG. 3 is a characteristic diagram showing the relationship between the gain control voltage Vout and FIG.
FIG. 3 is an input / output characteristic diagram of a transmission signal whose level is controlled by an ALC circuit. 4 to 7 show a conventional example.
The figure shows the circuit configuration when an ALC circuit is provided in the transmitter.
The figure is a characteristic diagram showing the relationship between the detection voltage Vin of the transmission signal and the gain control voltage Vout. FIGS. 6 and 7 are the input / output characteristic diagrams of the transmission signal whose level is controlled by the ALC circuit. 1 ALC circuit, 8 Gain control unit, 10 ALC amplifier, 12 Reference voltage setting unit, 16 Inverting amplifier, 18
Limiter circuit, Vref: Reference voltage, Vin: Detection voltage, V
out: Gain control voltage.

Claims (2)

(57) [Claims] 1. A pre-amplifier (2) for amplifying an input transmission signal with a constant gain and outputting the amplified signal, a detector (6) for detecting a voltage level of the transmission signal output from an antenna,
A transmitter comprising an automatic level control circuit (1) for controlling a voltage level of a transmission signal input from a preamplifier (2) based on a voltage level detected by a detection unit (6); ALC amplifier (10) that changes the gain for the transmission signal by the level control circuit (1)
A reference voltage setting unit (12) for setting a reference voltage for determining an operation point of voltage level control of a transmission signal; a voltage level of a transmission signal provided from the detection unit (6); and the reference voltage setting unit (12). Control that controls the upper limit value and the gain of the transmission signal voltage level in conjunction with each other so as to keep the ALC operating point (V _O ) of the ALC amplifier (10) constant based on the comparison result with the reference voltage given from A transmitter comprising: a gain control unit (8) for outputting a voltage. 2. A pre-amplifier (2) for amplifying an input transmission signal with a constant gain and outputting the amplified signal, a detector (6) for detecting a voltage level of the transmission signal output from the antenna,
A transmitter comprising an automatic level control circuit (1) for controlling a voltage level of a transmission signal input from a preamplifier (2) based on a voltage level detected by a detection unit (6); ALC amplifier (10) that changes the gain for the transmission signal by the level control circuit (1)
A reference voltage setting unit (12) for setting a reference voltage for determining an operation point of voltage level control of a transmission signal; a voltage level of a transmission signal provided from the detection unit (6); and the reference voltage setting unit (12). Control that controls the upper limit value and the gain of the transmission signal voltage level in conjunction with each other so as to keep the ALC operating point (V _O ) of the ALC amplifier (10) constant based on the comparison result with the reference voltage given from A gain control unit (8) for outputting a voltage; and the gain control unit (8) further inverts and amplifies a difference voltage between a detection voltage from the detection unit (6) and a reference voltage. Inverting amplifier that generates (16)
When the output voltage from the inverting amplifier (16) is higher than the reference voltage, the output voltage is held at a constant voltage level corresponding to the magnitude of the reference voltage, and this is output as a gain control voltage. On the other hand, if the output voltage from the inverting amplifier (16) is smaller than the reference voltage, the limiter circuit (1) outputs this output voltage as it is as the gain control voltage.
8) and a transmitter comprising: