JPH0152943B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a signal passing stage (mainly the first
In a noise blanker circuit that controls a noise gate installed at an intermediate frequency (intermediate frequency) to remove pulsed noise mixed in the received signal, large-amplitude noise pulses amplified in the noise amplification stage pass through the noise gate. The purpose is to prevent deterioration in the performance as a noise blanker due to the noise going around to subsequent signal circuits.

Noise blanker circuits are commonly used in high-sensitivity radio receivers, and are particularly effective at eliminating pulse noise.
Similar circuits are used in the AF stage of FM receivers, but here we are referring to the circuit that removes pulse noise in the original front stage, and an example of its general configuration is shown in Figure 1. It is desirable to remove unnecessary components other than the signal as much as possible in the front stage.The first reason is that the more circuits (especially active circuits) are stacked, and the more the amplitude is amplified, the more unnecessary components such as adjacent signals and noise will be removed from the received signal. Separation becomes impossible due to cross-modulation and intermodulation between the components, and secondly, the elapsed time of the pulse wave increases as it passes through a narrow filter between bands, making removal by blanking difficult. There is. Therefore, basically, as shown in the circuit configuration example in FIG.
A noise gate is placed at the output of the mixer, and the noise pulse is branched from the input side of the gate and passed through a noise amplification stage for noise rectification. In some cases, the signal is amplified to a certain polarity and level, and in some cases, a control pulse is generated using a Schmitt trigger, etc.), and during the period when the noise pulse passes through the gate, the gate is closed to prevent the noise pulse from passing. It is something to do. After passing through the gate, adjacent signals are removed through an IF filter with as narrow a band as possible for the signal to pass. Also in front of the gate
The main purpose of the IF filter is to provide a slight time delay to the signal circuit to match the timing with the gate control signal, and the bandwidth is several times larger than that of the main filter in the subsequent stage to reduce dulling of the pulse waveform.

When a noise blanker is placed before the IF in this way, the signal level is on the order of several tens of microvolts to mV. The noise pulses to be removed are those with peak values several times higher than the signal.
The noise amplification stage that amplifies this to the level of about 1V required for noise rectification needs to have a high amplification degree of 1000 to 1000 times, and when a particularly strong noise pulse is input, the noise amplification stage output will reach over 10V. Such high-level noise tends to leak into other circuits, and if it enters after the noise gate, it will destroy the effect of the noise blanker, so the noise amplification/rectification section should be strictly shielded, There are also gates and
There are restrictions such as having to keep it away from the IF circuit.

Figure 2 is a block diagram of a conventional circuit example of a noise blanker, in which 1 is a wideband IF filter, 2 is a noise gate, 3 is a narrowband IF filter, and 4 is a narrowband IF filter.
This is an IF amplification stage and has the same configuration as that shown in FIG.
Further, 5A is a noise amplification stage, 6 is a rectifier, and 7 is an AGC voltage amplifier for amplifying the DC component of the rectified output and applying AGC to the noise amplification stage. An AGC control voltage that is proportional to the average amplitude value regardless of the amplitude modulation degree is applied to the noise amplification stage, and the signal output is configured to be as constant as possible, and the threshold is set near the maximum value of the signal output. Noise pulses exceeding the level are detected, rectified, and applied to the gate control section 8A. An example of the operation of this circuit is shown in Figure 4A.
It is illustrated and shown in . In the figure, noise amplifier 5
is the IF signal input to A, and is the AGC (1) that operates with the rectified average value of the input signal, and AGC voltage amplifier 7
The AGC voltage sufficiently amplified by the noise amplification stage 5A
, the large-amplitude signal is suppressed and its output is equalized as a and b. On the other hand, the noise pulse has a very short duration, so even if the amplitude is several times larger than the signal, the average value is extremely small, so it hardly appears in the AGC(1) output, and therefore the noise pulse is fully amplified, and a large-amplitude pulse appears at the noise rectification output section from the latter stage of the noise amplification stage. The output of the gate control section 8A is. In this way, AGC is an average value type or a function close to an average value type, so
Since there is almost no AGC effect on very short-duration inputs such as noise pulses, the effects of large-amplitude noise pulses circulating to the stages after the noise gate are similar to those described in Figure 1. It is.

The present invention has been made in order to deal with such problems, and is aimed at controlling a noise gate provided in the signal passing stage of a radio receiver to remove pulse noise mixed in the received signal. In a circuit that separates noise pulses and performs noise gate control by multiplying the noise amplification stage of the noise blanker circuit by AGC that makes the signal output constant, 1
In addition to the above AGC, by providing a second AGC that reduces the output of noise pulses with an amplitude greater than a set value, large amplitude noise pulses in the noise amplification stage can be reduced.
This is a noise blanker circuit designed to reduce the possibility of pulses going around to the signal circuit after the noise gate.

FIG. 3 is a basic circuit block diagram explaining the principle of the present invention, in which 1 is a wideband IF filter, 2 is a noise gate, 3 is a narrowband IF filter, and 4 is a
This is an IF amplification stage and has the same structure as that shown in FIGS. 1 and 2. Further, 5B is a noise amplification stage, 6 is a rectifier, 7 is an AGC voltage amplifier for amplifying the DC component of the rectified output and multiplied by the first AGC (1) on the noise amplification stage 5B, and 8B is a gate control section. , 6 performs waveform shaping and other operations necessary to control the noise gate, and at the same time obtains the second AGC (2) output that operates with noise pulses of a certain amplitude or more. This is then passed through the AGC voltage amplifier 9 to the second noise amplification stage 5B.
By adding AGC, this configuration prevents large amplitude noise pulses from occurring after the noise amplification stage. In the figure, AGC(1) and AGC(2) are added separately to noise amplification stage 5B, but both
AGC may be synthesized and added to one location. An example of the operation of this circuit is illustrated in FIG. 4B. In the figure, when an IF signal containing noise pulses as shown in Figure 4B is input to the noise amplification stage 5B, the average value form AGC (1) becomes as shown below, and the AGC due to the noise pulses separated by the gate control section 8B is
(2) is. As a result of the operation of signal AGC (1) and pulse AGC (2) in the noise amplification stage, the noise and pulse outputs are made uniform as shown in '.

Claim 2 of the present invention presents a configuration of an AGC circuit that is effective in implementing the present invention.
That is, in Fig. 5, the rectified output of the noise amplification stage is applied to the base of the AGC transistor Q1 through an integral time constant circuit consisting of a resistor _R1 and a capacitor C, and the change in the collector potential is applied to the base of the AGC transistor _Q1 .
Configuration to supply as AGC and gate control transistor with diode _D1 connected in series to the emitter
Add the rectified output of the noise amplification stage to the base of Q ₂ ,
Connect the collector of Q ₂ and the collector of Q ₁ to the diode D ₂
This noise amplifier is characterized in that when a gate control pulse is generated, an AGC voltage ′ that operates on both the signal and the noise pulse is obtained at the collector of the AGC amplification transistor _Q1 .
It is a blanker circuit.

For example, if the integral type time constant circuit on the input side of the AGC amplification transistor Q ₁ is R ₁ = 10 kΩ, C = 10 μF, and time constant = 0.1 seconds, ripples of approximately 100 H ₂ or more are averaged, so Q ₁ The output amplified by
The pulse has been removed. Rectified output is applied to gate control transistor Q ₂ via resistor R ₂ ,
The initial voltage of diode D ₁ connected in series with the emitter (silicon diode is around 0.6V) is applied as a reverse bias, so together with the initial value of the base bias of Q ₂ (also around 0.6V), Since Q ₂ does not conduct at an input of about 1.2V or less, the peak of the signal output inside the AGC
If it is suppressed by (1), Q ₂ will not operate, and the output of Q ₂ will appear only by a noise pulse with a larger amplitude. A small resistor of 1 kΩ or less is used as the resistor R ₂ to prevent parasitic vibration, but if the rectified output is too large, a resistor value necessary for input level adjustment may be adopted. When Q ₂ is off, a conduction current flows from the power supply V _cc through resistor R ₅ to the gate diode of the noise gate section as indicated by the broken line arrow. (The noise gate section in the figure is shown in the simplest configuration in principle). When a noise pulse is input to Q ₂ and Q ₂ becomes conductive, the collector potential decreases as follows due to the voltage drop caused by resistor R _5. During that period, the gate diode becomes non-conductive and the noise gate function is suppressed. are doing. The present invention is characterized by a configuration in which the collectors of Q ₁ and Q ₂ are connected through a diode D ₂ when voltage changes are utilized for AGC of noise pulses. For D ₂ , the voltage change on the Q ₂ side is applied to the Q ₁ side, but the polarity is set so that the voltage _change on the Q ₁ side does not affect the Q ₂ side.・Diode, forward voltage drop of diode, and use these in series. As a result of the AGC voltage ' synthesized in this manner being applied to the noise amplification stage, even large-amplitude input pulses as shown in the top row of FIG. 6 are suppressed and made uniform. In Figure 5, Q ₁ and Q ₂ are originally necessary circuits for their respective applications, and by simply adding D ₂ to them, not only can the desired AGC operation be obtained, but also the AGC(1) and
There is an advantage that there is no need to consider mutual interference in a configuration in which AGC(2) is separately added to the noise amplification stage.

Claim 3 of the present invention presents another configuration example of the AGC circuit that is effective in implementing the present invention. That is, in Fig. 7, the rectified output of the noise amplification stage is applied to the base of the AGC transistor _Q1 through an integral time constant circuit consisting of a resistor _R1 and a capacitor C, and the change in the collector potential is supplied as the AGC of the noise amplification stage. By connecting a diode _D3 in parallel with the time constant resistor _R1 of the integral type time constant circuit of the first AGC amplifier _Q1 configured to The second one operates on noise pulses.
This is a noise blanker circuit that can be used commonly as AGC.

Regarding the operation of the first AGC, which has an integral time constant circuit consisting of a resistor _R1 and a capacitor C on the input side,
This is as detailed in the explanation of claim 2 above. In the present invention, by using a simple configuration in which a diode _D3 is connected in parallel with the time constant resistor _R1 , the collector of the AGC amplifier _Q1 is connected to the first AGC (1), which operates at the average value of the signal, and the signal whose amplitude is larger than that of the signal. It is possible to obtain a composite AGC voltage of the second AGC (2) that operates only with noise pulses.

D ₃ used here can be an ordinary small signal diode, and as is well known, silicon diodes have extremely low forward resistance, but below the initial conduction voltage (about 0.6V), they hardly conduct (equivalent to extremely high resistance). ), so the peak is 0.6V
For the following small amplitude inputs, it can be considered a circuit without _D3 . Therefore, AGC(1) is sufficiently effective and the rectified output of the signal is assumed to be _Q1 's initial bias of 0.6V.
If the voltage is suppressed to 1.2V or less, the operation for AGC(1) will be performed normally. Large amplitude inputs such as noise pulses pass through D ₃ and are added to the base of Q ₁ , but
When the capacitance of C is large, the rise of the waveform is delayed, so some resistance R may be inserted in series with C. In this case, the value of R is often selected to be around 1/10 of R ₁ within a range that does not significantly affect the time constant.
In such a circuit configuration, the operation of Q ₁ is as shown in Figure 8, since the collector potential of Q ₁ becomes the AGC voltage, large amplitude pulses in the noise amplification stage can be processed without any other changes or processing. It is something that can achieve the purpose of oppression. Furthermore, the seventh
In the figure, since _Q2 is dedicated to controlling the noise gate, there is an advantage that there is a large degree of freedom in the configuration of the gate control circuit.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of a noise blanker in a radio receiver, Fig. 2 is a block diagram of a configuration example of a noise blanker circuit, Fig. 3 is a block diagram showing a configuration of a noise blanker circuit of the present invention, and Fig. 4 The figure is the second
Fig. 3 is an operational waveform diagram of each part of the circuit, Fig. 5 is an example of an AGC circuit applied to the present invention, Fig. 6 is an operating waveform of each part of the circuit shown in Fig. 5, and Fig. 7 is an example of an AGC circuit applied to the present invention. FIG. 8 shows operating waveforms of various parts of the circuit shown in FIG. 7. 1.3...IF filter, 2...noise gate,
5A/5B... Noise amplification stage, 6... Rectifier, 7/9
...AGC amplifier, 8A/8B...gate control section, C
…Capacity, D・D ₁・D ₂・D ₃ …Diode, R・R ₁ .
R ₂・R ₃・R ₄・R ₅ …Resistor, Q ₁・Q ₂ …Transistor.

Claims (1)

[Claims] 1. A signal output to the noise amplification stage of a noise blanker circuit that controls a noise gate provided in the signal passing stage of a radio receiver to remove pulse noise mixed in the received signal. AGC in a constant format
In a circuit that performs noise gate control by separating noise pulses by multiplying A noise blanker circuit characterized in that a second AGC is provided to reduce the large amplitude noise pulse of the noise amplification stage from going around to the signal circuit after the noise gate. 2. A configuration in which the rectified output of the noise amplification stage described above is applied to the base of the AGC amplification transistor through an integral time constant circuit, and changes in the collector potential are supplied as the AGC of the noise amplification stage, and gate control with a diode connected in series to the emitter. By adding the rectified output of the noise amplification stage to the base of the transistor and connecting its collector to the collector of the AGC amplification transistor with a diode, a signal is sent to the collector of the AGC amplification transistor when a gate control pulse is generated. 2. The noise blanker circuit according to claim 1, wherein an AGC control voltage that operates on both noise pulses is obtained. 3 Integral type time constant of the first AGC amplifier configured to apply the rectified output of the noise amplification stage to the base of the AGC amplification transistor through an integral type time constant circuit, and supply the change in the collector potential as AGC of the noise amplification stage. A patent claim for a configuration that can be shared as a second AGC that operates with a noise pulse having a larger amplitude than the input signal amplitude and the initial conduction voltage of the diode by connecting a diode in parallel with the time constant resistance of the circuit. The noise blanker circuit described in item 1.