DE4042047A1 - Voltage control amplifier with differential transistor pairs - has emitter magnitude of one transistor pair as multiple of other transistor pair emitter magnitude - Google Patents

Abstract

The transistor differential pairs are in common coupled to emitters, and an input signal is applied to a common connection for the emitters. The base potential of first transistors of the pairs is controlled for deriving a variable output signal by changing the current balance of the transistor pairs. The magnitude of the emitters of the first transistors (Q1,4) is a multiple of the emitter magnitude of the second transistors (Q2,3), with the multiple being a natural number exceeding unity. Pref. the emitter magnitude of the first transistors is the emitter surface in one transistor, possibly a surface of an emitter diffusion face on an integrated circuit chip. USE/ADVANTAGE - For noise suppression in FM tuner, or magnetic tape recorder, with attentuation adjustment without regard to control voltage changes.

Description

The present invention relates to a voltage controlled amplifier (VCA), specifically to one those intended for use in a noise reduction system an FM tuner or a tape recorder.

When an FM stereo broadcast using an FM tuner received, interference due to Multipath propagation of the signal result from the location depend on where the antenna is or on the level of the electric field generated by the transmitter. Furthermore, interferences mix, such as Tape noise, undesirable when playing tape a tape recorder in the signal. To murmur the described Kind to decrease, or to reduce the dynamic range of the To enlarge playback signals is the audio component with provided a noise reduction system.

As an example of a noise reduction system as described Art has been proposed a structure in which the level of Output signal depending on the level of the input signal being affected. In addition, the influence on the Hearing sensitivity, which is due to the level difference between the playback signal and the noise can be exploited, so that the noise is reduced. The one described above Construction uses the voltage controlled amplifier for Influencing the level of the output signal described above.

For the voltage controlled amplifier for use in the conventional noise reduction system becomes the influencing input voltage as the input voltage  Input connection of the voltage controlled amplifier via a Buffer amplifier supplied. A control voltage generation circuit receives the quadratic mean or the Peak level of the input voltage to use it as the control voltage Control voltage input of the voltage controlled amplifier feed. The voltage controlled amplifier transmits the Output voltage whose level is in accordance with the Control voltage, d. H. the level of the input voltage has been.

Fig. 4 shows schematically the structure of a voltage controlled amplifier for use in a conventional noise suppression system. With reference to FIG. 4, the input voltage V ₁ to be influenced is supplied as an input voltage V _{IN to} an input terminal of a voltage-controlled amplifier 2 via a buffer amplifier 1 . A control voltage generating circuit 3 receives the root mean square or the peak value of the input voltage V _IN in order to supply it as a control voltage V _{C to} a control input terminal of the voltage-controlled amplifier 2 . The voltage controlled amplifier 2 transmits the output voltage V _OUT , the level of which has been influenced in accordance with the control voltage V _C , ie in accordance with the level of the input voltage V _IN .

Fig. 5 shows an electric circuit of a conventional voltage-controlled amplifier 2.

The voltage-controlled amplifier 2 is constructed in such a way that a transistor differential pair consisting of transistors Q ₁ and Q ₂ and a further transistor differential pair consisting of transistors Q ₃ and Q _{4 are} operated in parallel. In addition, the electric current balance (double balance) between the transistors Q ₁ and Q ₄ and that between the transistors Q ₂ and Q _{3 is changed} by the control voltage V _C such that the gain (i ₀ / i), which is in accordance with the Ratio of the input current i to the output current i _{0 is} determined, is obtained. Referring to FIG. 5, reference numerals 5 and 9 represent electrical current sources, the electrical current sources 6 and 7 forming a current mirror circuit and V _{REF being} a reference voltage.

. In the voltage-controlled amplifier 2, using a transistor differential pair of Figure 5, voltages V _{BE1 4} can be respectively expressed by the following equations of the transistors Q ₁ to Q to V _BE4 between the bases and the emitters of:

in which:

K: Boltzmann constant
T: Absolute temperature
q: amount of electron charge
I _S : Reverse saturated current
I _C1 to I _C4 : collector currents

From equations (1) to (4), one can do the following Get context:

The following relationships apply in this state:

I _C1 + I _C2 = I + i (7)

I _C3 + I _C4 = I (8)

Therefore, by inserting equations (7) and (8) into equations (5) and (6) achieve the following relationship:

where I _C2 and I _{C4 can} each be expressed as:

The following output current flows through the output connector:

The gain of the voltage controlled amplifier 2 is therefore given by the following equation:

If the control voltage V _C = 0, then the gain of the voltage-controlled amplifier 2 has the following value:

Figure 6 shows the input / output characteristics of the voltage controlled amplifier of the type described above. As shown in Figure 6, the attenuation of the conventional voltage controlled amplifier is set to about -60 dB when the input voltage V _IN = 0 volts. In the event that the voltage controlled amplifier thus configured is used in the noise suppression system, the noise contained in the output is attenuated by approximately -60 dB compared to a predetermined input when the input has no signal (including noise).

As shown by the broken line in Fig. 5, a level shift of the voltage Va between the input voltage V _IN and the control voltage V _{C is} generated when the output voltage V _OUT in the voltage controlled amplifier 2 shown in Figs. 4 and 5 is obtained by changing the control voltage V _C for determining a noise level of, for example, V _OUT = -14 dB (or -20 dB) in a signal-free state (V _IN = 0). Even with a shift of only 10 mV of the voltage Va, there is a real possibility that a shift of more than ± 3 dB is produced, assuming that Va = 100 mV. A problem therefore arises in that the gain of the voltage controlled amplifier is undesirably changed with respect to a predetermined control voltage. In order to overcome this problem, level adjustment must be carried out by supplying the voltage Va from a level shift current source 4 and inserting resistors 10 and 11 or the like in places above the voltage controlled amplifier 2 .

The gain of the conventional voltage controlled amplifier 2 can be obtained from equation (14), and the gain in the signal-free state (V _C = 0) is 1/2. When V _C = 0, the influence of changes in voltage and electric current of the control voltage generating circuit on the voltage controlled amplifier 2 can be prevented satisfactorily.

That is, although the voltage controlled amplifier is capable of precisely controlling a damping amount of - ∞, -6 dB or 0 dB, a control voltage V _{C of} a level -V _BE or less becomes 0 V (grounded voltage) or V _BE or more usually delivered. However, there is a desire to change the attenuation from -20 dB to 0 dB. According to the example described above, V _C must be changed from 10 mV to a level that exceeds V _BE (about 700 mV). However, it is difficult to generate the 10 mV level control voltage. What is worse, when the 10 mV level is reasonably safely reached, there is still the problem that the gain of the voltage controlled amplifier becomes -20 dB. The gain of the voltage controlled amplifier is set to an unsafe level between -30 dB and -15 dB at about 10 mV. The desired voltage-controlled amplifier with an attenuation that lies between -20 dB and 0 dB cannot therefore be obtained.

An object of the present invention is to provide one voltage controlled amplifier to be specified for use in a noise reduction system is suitable and in the Is able to change the damping regardless of the Adjust control voltage or the like.

One aspect of the present invention is in one voltage controlled amplifiers with transistor differential pairs, of which the emitters are connected and in which an input signal is fed to a common connection, to which the emitters are connected, and the base potential which becomes a transistor of the transistor difference pairs controlled, whereby a variable output signal is obtained, by the current balance (current balance) of the transistor difference pairs is changed, the voltage controlled  Amplifier has an improvement in that the size the emitter of a transistor is set up so that it is n times the size of the emitters of the other transistors, where n is an integer greater than 0.

According to the present invention, the size of the emitters is one transistor n times that of the other transistors. The damping of the voltage controlled amplifier is therefore only determined by the physical dimensions of the transistors.

The attenuation that is suitable for the noise reduction system is can therefore be obtained exactly and as desired without to be affected by the change in control voltage by choosing the number n of the emitter size factor accordingly becomes.

The invention is described below with reference to the Drawings explained in more detail. It shows

Fig. 1 shows an electrical circuit of a first embodiment of the invention;

Fig. 2 is an electric circuit of another embodiment of the invention;

Fig. 3 is an electric circuit of a third embodiment of the invention;

Fig. 4 is a block diagram of a voltage controlled amplifier for use in a conventional noise reduction system;

Fig. 5 is an electric circuit of a conventional voltage-controlled amplifier;

Fig. 6, the input / output characteristic of the conventional voltage-controlled amplifier of Fig. 5; and

Fig. 7 is a block diagram of another conventional structure.

Fig. 1 shows an electric circuit of a voltage-controlled amplifier according to the present invention. Elements which are comparable to those according to FIG. 5 have the same reference symbols and are not explained again here.

The voltage-controlled amplifiers of FIG. 1 is configured such that the size of the emitter of each of the transistors Q ₁ to Q _4, the n-fold of that of the transistors Q ₂ and Q _3, where a real number n is greater than 1. The emitter size can be adjusted by multiplying the area of the emitter diffusion area formed on an IC chip by n. Another method, which is shown in FIG. 2, provides that transistors Q ₁₁ to Q _1n and Q ₄₁ to Q _{4n are formed in} parallel on the IC chip in order to use the total area of the emitters in the same way. fold. Since the same characteristic can be achieved with both methods, one of the methods can be used here.

The gain of the voltage-controlled amplifier according to FIG. 1 is then obtained . The voltage _levels V _BE1 to V _BE4 between the base and the emitter of each of the transistors Q ₁ to Q ₄ can be expressed as follows:

The equations (16) to (19) derived in this way are in each case solved by comparable calculations to those above Equations (5) to (13) described. As As a result, the current flowing through the output connector flows as follows:

In this case the gain is obtained as:

If V _C = 0, then the gain becomes:

You can therefore a desired gain by appropriate Setting the multiplication factor n of the emitter size achieve.

Fig. 3 shows a special structure when the emitter size of the transistors Q ₁ and Q _{4 is set} to four times (n = 4) the emitter size of the transistors Q ₂ and Q ₃ . Fig. 3A shows a case in which V _C = 0 V. In this state, since the output current i ₀ and the input current i satisfy the equation i ₀ = i, the gain (i ₀ / i) becomes 1/5, ie the attenuation becomes -14 dB. On the other hand, Fig. 3B shows the case, in which V _C = -V _X, wherein _X indicates the -V voltage is cut off by the transistors Q _1, and Q _4. In this state, since the output current i ₀ and the input current i fulfill the condition i ₀ = 5i, the gain (i ₀ / i) becomes 1, ie the attenuation becomes 0 dB. The controllable range of variation of the voltage-controlled amplifier is therefore between V _C = 0 and V _C = -V _X.

As described above, the voltage controlled amplifier according to the invention is suitable for use in an IC process in which the emitter size can be easily adjusted. The emitter size is determined in the IC manufacturing process for the purpose of obtaining a predetermined amount of attenuation when V _C = 0. Furthermore, the usual need to perform level adjustment can be eliminated. As a result, the attenuation can be easily and precisely adjusted to suit the noise reduction system.

As mentioned above, according to the present invention, a voltage controlled amplifier can be easily obtained for a noise reduction system is suitable by a predetermined gain for the voltage controlled Amplifiers can be obtained with accuracy and not is influenced by small changes in the control voltage.

Claims (5)

1. Pair voltage controlled amplifiers with transistor difference to which the emitters are commonly connected and an input signal is applied to a common connection to which the emitters are connected, the base potential of one of the transistors of the transistor difference pairs being controlled, whereby a variable output signal is obtained by Change in the current balance (current balance) of the transistor differential pairs, characterized in that the size of the emitters of the one transistors (Q ₁ , Q ₄ ) is n times (n is a natural number greater than 1) the size of the emitters of the other transistors ( Q ₂ , Q ₃ ). 2. Voltage controlled amplifier according to claim 1, characterized in that the size of the emitter of one Transistors is the area of the emitter in a transistor.   3. Voltage controlled amplifier according to claim 2, characterized in that the size of the emitter of Transistors the area of an emitter diffusion area on a IC chip is. 4. Voltage-controlled amplifier according to claim 1, characterized in that a plurality of transistors (Q ₁₁ to Q _1n , Q ₄₁ to Q _4n ) are arranged in parallel to the total size of the emitter of the one transistors (Q ₁₁ to Q _1n , Q ₄₁ to Q _4n ) to make n times the size of the emitters of the said transistors (Q ₂ , Q ₃ ). 5. Voltage-controlled amplifier according to claim 4, characterized in that the transistors (Q ₁₁ to Q _1n , Q ₄₁ to Q _4n ) are arranged in parallel to the total area of the emitter of the one transistors (Q ₁₁ to Q _1n , Q ₄₁ to Q _4n ) to make n times the size of the emitters of the other transistors (Q ₂ , Q ₃ ).