JPH0468922A - Automatic level control circuit - Google Patents

Abstract

PURPOSE:To facilitate an adjustment control by controlling an upper limit limiting the voltage level of a transmission signal and a gain with respect to the transmission signal interlockingly with each other. CONSTITUTION:Since the absolute level of a gain control voltage Vout is changed by varying a reference voltage Vref, the upper limit of a transmission signal to obtain the operating point of a limiter circuit 18 is changed as L1 L2 L3. Simultaneously, since the voltage level of the operating point when the diode D1 of the limiter circuit 18 is turned on/off attended with the change in the reference voltage Vref is also changed, the gain of an ALC amplifier 10 is changed as G1 G2 G3. Thus, when the reference voltage Vref is adjusted, since the upper limits L1-L3 of the voltage level with respect to the transmission signal and the gains G1-G3 are controlled interlockingly with each other, the adjustment of them is facilitated.

Description

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

<Prior Art> Generally, in the communication field, various upper limit values of the voltage level of the transmitted signal are standardized depending on the transmission frequency. Therefore, in transmitters etc., the voltage level of the transmitted signal exceeds the upper limit value An automatic level control circuit (hereinafter referred to as an ALC circuit) is provided to control the level so as not to exceed the level.

FIG. 6 shows a conventional example in which a transmitter is provided with an ALC circuit. In the figure, lo is an ALC circuit, 2o is a front-stage amplifier whose gain can be adjusted, 3 is a power amplifier, and 4 is an antenna. In this example, the above-mentioned ALC circuit to detects the voltage level of the transmission signal and detects the corresponding detection voltage Vi.
a detection unit 6 that outputs n, a volume VR as a reference voltage setting unit for setting a reference voltage V ref that determines the operating point of the level control of the transmission signal, and a detection voltage Vin from the detection unit 6 and the reference voltage. It consists of a gain control unit 8° that generates a gain control voltage Vout based on a comparison result with Vrer, and an ALC amplifier IO whose gain changes according to the magnitude of this gain control voltage Vout.

The gain control unit 8° is composed of, for example, an operational amplifier, and has voltage input/output characteristics shown in FIG. That is, the detection voltage Vin from the detection unit 6 is the reference voltage V rer
(V in<V ref), the gain control section 8° always outputs the gain control voltage V out at a constant level. Therefore, the gain of the ALC amplifier 10 is also kept constant (for example, CO). On the other hand, if the detection voltage Vin exceeds the reference voltage Vref (V
in≧V rer), the gain control unit 8° outputs a gain control voltage V that is inversely proportional to the magnitude of the detected voltage Vin.
out is output. Therefore, as the detection voltage Vin increases, the gain control voltage V out gradually decreases, and the gain of the ALC amplifier 10 decreases accordingly. As a result, as shown in FIG. 6, the ALC circuit l. When the voltage level of the transmission signal input to the ALC circuit 1 exceeds a predetermined threshold value (for example, Vυ), the voltage level of the transmission signal output from this ALC circuit 1° exceeds the upper limit value (for example, L
L).

<Problems to be Solved by the Invention> As mentioned above, there are various standard values for the voltage level of the transmission signal.
As shown in the figure, it may be necessary to reset the upper limit of the voltage level limited by the ALC circuit to L, -L, -L3.

This adjustment is performed by operating the volume VR, to adjust the reference voltage V.
This is done by changing the value of ref, but the upper limit is set to L.

-1, -L3, the gain of the ALC amplifier 10 remains constant (-G) until the voltage level of the transmission signal reaches each threshold voltage (V9, -3). ), whereas each threshold voltage is ■.

It becomes smaller as →■,→V3. This is ALC
circuit l. The lower the upper limit of L l-L t→L3, the lower the dynamic range of the transmitted signal becomes R,-+-Rt
- means narrowed to Rs. Therefore, when the upper limit value is set to a small value (for example, L3) in accordance with the standard, an inconvenience arises in that an effective signal cannot be transmitted.

ALC circuit l. After setting the upper limit value to a predetermined value (for example, L3), in order to secure the required dynamic range, as shown in FIG. , and adjust the gain to G. -G + -G t, but if you make the gain too small (for example, G3),
ALC circuit l. Before the voltage level is limited by , distortion occurs in the transmitted signal (■ in FIG. 7. Distortion occurs at a voltage higher than 1), and linearity is impaired.

As described above, conventionally, in order to ensure the required dynamic range for the transmission signal and to prevent distortion from occurring, the pre-stage amplifier 20 and the ALC circuit l are used. It is necessary to adjust each volume individually, making the adjustment operation complicated.

<Means for Solving the Problems> The present invention has been made in view of the above circumstances, and provides a method in which the upper limit value for limiting the voltage level of the transmission signal and the gain for the transmission signal are controlled in conjunction with each other. In other words, by setting the upper limit value, an appropriate gain is uniquely determined, thereby making the conventional adjustment operation easier.

Therefore, the present invention includes a reference voltage setting section 12 that sets a reference voltage, and a gain control that generates a gain control voltage based on a comparison result between the voltage level of a transmission signal and the reference voltage set by the reference voltage setting section. 8 and an ALC amplifier IO that changes the gain for the transmission signal according to the gain control voltage from the gain control section 8. The ALC circuit has the following configuration.

That is, in the present invention, the gain control section 8 of the ALC circuit is controlled by the inverting amplifier 16 that inverts and amplifies the transmission signal with a gain corresponding to the magnitude of the reference voltage given from the reference voltage setting section 12, and from this inverting amplifier 16. The inverting output of the inverting amplifier 16 is compared with the reference voltage, and if the output voltage of the inverting amplifier 16 is larger than the reference voltage, the output voltage of the inverting amplifier 16 is maintained at a constant voltage level according to the magnitude of the reference voltage. It is composed of a limiter circuit 18.

Function> In the above configuration, the reference voltage setting section I2 sets the reference voltage V
When ref is set, an output voltage Vx is generated from the inverting amplifier I6 by inverting and amplifying the transmission signal with a gain corresponding to the magnitude of the reference voltage V ref. The limiter circuit 18 operates when the output voltage Vx from the inverting amplifier 16 is larger than the reference voltage V ref (VW≧v ref).
, the output voltage Vx from the inverting amplifier 16 is held at a constant voltage level according to the magnitude of the reference voltage V rcJ and output as the gain control voltage VOut, while the output voltage Vx from the inverting amplifier 16 is set to the reference voltage V ref (Vx<Vref), this output voltage Vx is output as is as the gain control voltage Vout.

Then, the gain control voltage V ou with such characteristics is
Since t is grouped with ALC amplifier l, when the voltage level of the transmission signal is lower than the reference voltage V ref,
The gain control voltage v out is constant and the ALC amplifier I
The gain of O is kept constant.

On the other hand, when the voltage level of the transmission signal exceeds the reference voltage V rcJ, the gain control voltage v out gradually decreases accordingly, so the gain of the ALC amplifier IO also decreases.
The voltage level of the transmitted signal will be maintained at a constant value.

Further, when the reference voltage V rer is changed, the output voltage Vx of the inverting amplifier 16 changes accordingly, and at the same time, the voltage level at the operating point of the limiter circuit 18 also changes. That is, when the reference voltage Vref is changed, the gain control voltage V
Since out changes, the gain of the ALC amplifier IO is also changed, and the upper limit value of the transmission signal determined by the operating point of the limiter circuit 18 is also changed.

In this way, by simply adjusting the reference voltage V ref, the upper limit value of the voltage level and the gain for the transmission signal are controlled in conjunction with each other, making it easy to adjust both, and also to ensure that the transmission signal is always It becomes possible to secure the required dynamic range and limit the voltage level to an appropriate level that does not exceed the standard value.

<Embodiment> FIG. 1 is a circuit configuration diagram when a transmitter is provided with an ALC circuit, and parts corresponding to the conventional example shown in FIG. 4 are given the same reference numerals. In FIG. 1, I is an ALC according to the present invention.
In the circuit, 2 is a preamplifier set to a constant gain, 3 is a power amplifier, and 4 is an antenna.

The above ALC circuit 1 includes a detection unit 6 that detects the voltage level of the transmission signal and outputs a detection voltage Vin corresponding to the voltage level of the transmission signal;
Reference voltage V r that determines the operating point of level control of the transmission signal
A reference voltage setting unit 12 for setting eJ, a gain control unit 8 that generates a gain control voltage V out based on a comparison result between the detection voltage Vin from the detection unit 6 and the reference voltage V ref, and this gain control voltage. It consists of l groups of ALC amplifiers whose gain changes according to the magnitude of V out.

In this example, the above gain control section 8 converts the detection voltage Vin into a reference voltage V ref given from the reference voltage setting section 12.
An inverting amplifier 16 that performs inverting amplification with a gain corresponding to the magnitude of
When it is larger than reJ, a limiter circuit 18 that maintains the output voltage Vx at a constant voltage level according to the magnitude of the reference voltage V ref and an ALC
Amplifier 20 that adjusts to a voltage level suitable for gain control of amplifier IO and outputs it as gain control voltage V out
It consists of The inverting amplifier 16 includes an operational amplifier Amp1 and resistors R1 to R4, and the limiter circuit 18 includes an operational amplifier Amp, a diode D1, and resistors R6 to R6.

Next, the operation of the ALC circuit 1 having the above configuration will be explained with reference to FIGS. 2 and 3.

When transmitting a transmission signal from the antenna 4, a detection voltage Vin corresponding to the voltage level of the transmission signal is generated from the detection unit 6, and this detection voltage Vin is applied to the anti-phase input terminal of the operational amplifier Asp+ constituting the inverting amplifier I6. Added to (-). Since the reference voltage VrcJ is applied to the positive phase input terminal (+) of the operational amplifier Ai+p+, the operational amplifier Asp
, an output voltage VW is generated by inverting and amplifying the detection voltage Vin with a gain corresponding to the reference voltage V rer. Therefore, as shown in FIG. 2, this output voltage Vx is inversely proportional to the detected voltage Vin. and,
The output voltage VX of the inverting amplifier 16 is passed through the resistor R6 of the limiter circuit 18 to the negative phase input terminal (
). Since the reference voltage V ref is applied to the positive phase input terminal (+) of the operational amplifier A lpt,
When the above output voltage Vx is larger than the reference voltage Vref (VW≧V ref), the output of the operational amplifier A11)t becomes negative, and a current flows through the diode D. Therefore, the output voltage VW of the inverting amplifier 16 is maintained at a constant voltage level depending on the magnitude of the reference voltage V ref. Since this constant level output voltage VX is applied to the ALC amplifier 10 as the gain control voltage VOut via the amplifier 20, the gain of the ALC amplifier 10 becomes constant. Therefore, when the voltage level of the transmission signal is small and therefore the output voltage Vx of the inverting amplifier 16 is larger than the reference voltage V rer (VX≧V reD, the transmission signal input to the ALC amplifier 10 has a constant gain. It will be amplified.

On the other hand, the voltage level of the transmission signal is high, and therefore the output voltage Vx from the inverting amplifier 4 summer 6 becomes the reference voltage Vr.
When the voltage becomes lower than er (V x < V ref), the output of the operational amplifier Amp becomes positive and the current flowing through the diode D is cut off. It is directly applied to the ALC amplifier 10 as a gain control voltage Vout. Therefore, the voltage level of the transmitted signal gradually increases,
As a result, the output voltage VW of the inverting amplifier 16 becomes the reference voltage V
If it becomes below re4, the gain control voltage V will be adjusted accordingly.
Since out also gradually decreases, the gain of the ALC amplifier 10 also decreases, and is maintained at a constant value so that the voltage level of the transmission signal does not exceed the upper limit.

On the other hand, as shown in FIG. 2, the reference voltage set by the reference voltage setting section 12 is, for example, V rer , -1-V
er, -+Vre, etc., the inversion gain of the inverting amplifier 16 with respect to the detection voltage Vin also gradually decreases, and accordingly, the output voltage Vx gradually decreases. Therefore, by changing the reference voltage V reJ,
Since the absolute value level of the gain control voltage Vout changes, the upper limit value of the transmission signal that determines the operating point of the limiter circuit I is changed to -"Ll-'Lt" as shown in FIG. As the reference voltage V rer changes, the voltage level at the operating point that turns on and off the diode D of the limiter circuit 18 also changes, so the gain of the ALC amplifier 10 changes from G1 → Gt → G. Become.

In this way, when the reference voltage V rer is adjusted, the upper limit value of the voltage level for the transmission signal 1 to L3 and the gains G, to G are controlled in conjunction with each other, so that adjustment operations for both become easier. Moreover, the operating point V0 of the level control of the transmission signal is the upper limit L, as shown in FIG.
Since it is always constant without being affected by the setting of t''Ls, this operating point ■.

By setting the voltage in advance to a level that does not cause signal distortion, you can always ensure the required dynamic range for the transmitted signal, and set the appropriate voltage without causing signal distortion or exceeding the standard value. level can be restricted.

<Effects of the Invention> According to the present invention, the upper limit value of the voltage level and the gain for the transmission signal are controlled in conjunction with each other by simply adjusting the reference voltage, so the adjustment operation for both is easier than in the past. become. In addition, it is possible to always secure the required dynamic range for the transmitted signal, and furthermore, it is possible to limit the voltage to an appropriate voltage level that does not exceed the standard value without causing signal distortion. Excellent effects are demonstrated.

[Brief explanation of drawings]

1 to 3 show embodiments of the present invention, and FIG. 1 is a circuit configuration diagram when the transmitter is provided with an ALC circuit;
Figure 2 shows the detected voltage V of the transmitted signal when changing the reference voltage.
A characteristic diagram showing the relationship between in and gain control voltage vout,
FIG. 3 is an input/output characteristic diagram of a transmission signal whose level is controlled by an ALC circuit. Figures 4 to 7 show conventional examples. Figure 4 is a circuit configuration diagram when the transmitter is provided with an ALC circuit, and Figure 5 shows the detection voltage Vin of the transmission signal and the gain control voltage V out.
FIGS. 6 and 7 are input/output characteristic diagrams of a transmission signal whose level is controlled by an ALC circuit. l...ALC circuit, 8...gain control section, IO...
・AL C amplifier, 12... Reference voltage setting section, 16.
...Inverting amplifier, 18...Limiter circuit, V ref
...Reference voltage, Vin...Detection voltage, V out
Gain control voltage.

Claims (1)

[Claims] (1) A reference voltage setting unit (12) that sets a reference voltage that determines the operating point of voltage level control of the transmission signal, and generates a gain control voltage based on a comparison result between the voltage level of the transmission signal and the reference voltage. A gain control section (8) and an ALC amplifier (1) that changes the gain for the transmission signal according to the magnitude of the gain control voltage from the gain control section (8).
0), wherein the gain control section (8) inverts and amplifies the transmission signal with a gain corresponding to the magnitude of the reference voltage given from the reference voltage setting section (12). The output voltage from the inverting amplifier (16) and the reference voltage are compared, and if the output voltage of the inverting amplifier (16) is greater than the reference voltage, the inverting amplifier (16) An automatic level control circuit comprising: a limiter circuit (18) that maintains the output voltage of the output voltage at a constant voltage level according to the magnitude of a reference voltage.