JPH0528837Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a data receiving device with a wide dynamic range, and particularly to an automatic S/N improvement circuit.

[Conventional technology]

Conventionally, data receiving devices with a wide dynamic range have used a normal AGC loop in consideration of the input level range and threshold level to set an optimal level diagram that does not become saturated with noise.

FIG. 4 shows a typical AGC loop, which consists of an AGC amplifier 2, a level detector 4, a loop filter 5, and a DC amplifier 6. 9 is a demodulator.

[Problem that the invention attempts to solve]

By the way, in a receiving device having this type of AGC loop, the wider the dynamic range and the lower the threshold level, the more the AGC amplifier 2
Since the fixed level of the output becomes absolutely low, there is a drawback that the demodulation S/N is low even when a strong signal is input.

This is because, as shown in Figure 5, the S/N of the receiver demodulated output has an upper limit at the ratio of the output level of the AGC amplifier to the noise level determined by the subsequent NF (noise figure). Particularly when receiving and demodulating frequency modulated waves, there have been cases where the required S/N cannot be obtained.

In addition, in order to improve this, we have added
Even if we tried to reduce the NF, the actual situation was that we could only obtain an improvement of a maximum of several dB.

[Means for solving problems]

The present invention includes a programmable attenuator whose gain or attenuation is determined by an external control signal, a means for comparing the AGC voltage with a predetermined reference voltage, and an output signal of the comparison means in a normal AGC loop. and a level converter for converting the signal into the external control signal.

[Effect]

The present invention reduces the gain between the AGC amplifier and the level detector using the programmable attenuator above a certain required reception level from the AGC voltage corresponding to the reception level, and equivalently reduces the AGC amplifier output level (constant level). ) is increased by the amount of gain reduction, thereby reducing the S/N when receiving a strong signal.
This is a major improvement.

〔Example〕

FIG. 1 shows an embodiment of the present invention. 1 is a reception input terminal, 2 is an AGC amplifier, 3 is a programmable attenuator, 4 is a level detector, 5 is an AGC loop filter, 6 is a DC amplifier, 7 is a comparator with hysteresis characteristics, 8 is a level converter, 9 is a In the demodulator, 10 is a demodulation output terminal.

The received signal input level is L _a in Figures 2 and 3.
In the following cases, the reference voltage of comparator 7 is set to the reception level L _b , and level converter 8
The programmable attenuator 3 enters the through (ATT OFF) state by the output of , and performs normal AGC loop operation. From that state, the reception level
When L _b is exceeded, the programmable attenuator 3 is turned on (ATT ON) by the comparator 7. At this time, the level of the input of the level detector 4 decreases by the amount of insertion ATT, but the AGC loop keeps the input of the level detector 4 at the nominal level.
Controls AGC amplifier 2, and its output level is inserted
Increases by ATT. (See Figure 3) Therefore, the demodulation S/N of the output terminal 10 in this state is the AGC
The improvement will be due to the increase in the output level of the amplifier 2. At this time, the reference voltage of the comparator 7 is changed to the reception level L _a , and _the programmable attenuator 3
is in the on (ATT ON) state.

[Effect of idea]

As explained above, the present invention has the advantage of being able to automatically improve demodulation S/N with a relatively simple hardware configuration. Therefore, the present invention has a wide dynamic range and is suitable for PM, FM,
It is particularly effective for general-purpose receivers that can support various modulation types such as AM.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the present invention;
The figure is a diagram for explaining the operation of the comparator 7 in Figure 1, Figure 3 is an S/N characteristic diagram for explaining the operation of the embodiment of the present invention, and Figure 4 is a diagram for explaining the operation of the comparator 7 in Figure 1.
A block diagram of the AGC loop, and FIG. 5 is an S/N characteristic diagram for explaining the operation of FIG. 4. In the figure, 2...AGC amplifier, 3...Programmable attenuator, 4...Level detector, 5...AGC
Loop filter, 6... DC amplifier, 7... Comparator, 8... Level converter, 9... Demodulator.

Claims (1)

[Scope of utility model registration request] an AGC amplifier that receives an input signal and suppresses the level change to a constant level; a level detector that detects the output level of the AGC amplifier; a loop filter connected to the level detector; A programmable attenuator, the gain or attenuation of which is determined by an external control signal, is provided between the AGC amplifier and the level detector in the AGC loop including a DC amplifier that controls the AGC amplifier using the AGC voltage. and further comprising: means for comparing the AGC voltage with a predetermined reference voltage; and a level converter for converting the output signal of the comparing means into the external control signal. N improvement circuit.