JPS6041899B2 - Analog signal processing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an analog signal processing device in devices that transmit and receive analog signals, such as magnetic recording and reproducing devices such as audio tape recorders and video tape recorders, and transmitting and receiving devices such as transceivers. The purpose is to expand the dynamic range.

In general, in a magnetic recording/reproducing device, the size of the dynamic range is cited as a factor that determines the performance of the device.

Dynamic range is the ratio between the maximum output and the minimum output at which a signal can be heard normally. However, since low-level signals are generally masked by the noise level and become inaudible, the dynamic range is the ratio between the maximum output and the noise level. You can see it. Therefore, in the case of magnetic recording and reproducing devices, expansion of the evening range is done by using low-noise recording media or by utilizing low-noise devices, but this type of method is insufficient. I couldn't get any good results. The dynamic range of the human ear is 120dB.
Considering that general magnetic recording and reproducing devices have a maximum performance of about 8 B, it has been desired to develop a new method for expanding the dynamic range. The present invention can fully satisfy the demands of this era, and one embodiment thereof will be described below with reference to the drawings. FIG. 1 shows the configuration of the device of this embodiment.
Reference numeral 1 denotes a terminal to which an analog signal such as an audio signal is input, and to this terminal 1, an analog signal subjected to band restriction necessary for sampling is input.

This input analog signal is sampled by a sample-and-hold amplifier 2, that is, an amplifier that holds the sampled level until the next sampling. is applied to Here, the analog-to-digital converter 4 is operated twice within one sample period of the sample-and-hold amplifier 2. That is, it is first used to identify the level of the input analog signal. In this case, variable gain amplifier 3 performs 1x amplification. In other words, level detection is performed by directly converting the level value sampled and held by the sample-and-hold amplifier 2 from analog to digital, and the digital output signal of the analog-to-digital converter 4 at this time is sent to the next-stage latch circuit. 5 and is input to the level identification logic circuit 6, and this circuit 6 presets the level. - The level is determined by comparing with the specified value. As a result of this level discrimination, for example, when the level of the input analog signal is equal to or higher than the maximum human input signal level of 114 (-12 dB), the variable gain amplifier 3 maintains its amplification factor at 1, and the input signal is once again converted into an analog signal. The output of the analog◆digital converter 4 is input to the latch circuit 5. When the input signal level is below the maximum human signal level of 114, the output of the analog ◆ digital converter 4 is input to the latch circuit 5.
2 dB), and analog-to-digital conversion is performed once again with the amplification degree of the q variable gain amplifier 3 quadrupled. The above operation is called analog compression, and the result is the ratio of the input signal level to the noise level (S
/N), the relationship is as shown in Figure 2. That is, assuming that the noise level is constant, the S/N becomes the maximum (point A) when the human input signal level is the maximum (point O). When the input signal level decreases, the S/N also deteriorates, and if analog compression processing as described above is not performed, the characteristic will be A-B. However, when analog compression is performed, for example, the input signal level becomes 114 (-1), which is the maximum human input signal level.
2 dB) level (point E), the input signal of the analog-to-digital converter 4 is quadrupled (12 dB) by the variable gain amplifier 3, and the S/N also improves (point D).
. As a result, the overall characteristics become A-C-D-B'', and the dynamic range of the input signal also changes from O-B to O-
The dynamic range expands by 12 (1B) between B''. If analog compression is performed in this way, the dynamic range can be expanded by the amplification degree of the variable gain amplifier 3, but on the other hand, the dynamic range The more you widen the S/N ratio at point E in Figure 2, the more the discontinuity C-
D becomes larger. This problem is solved by digital compression/expansion processing, which will be described later. After analog compression, analog
The digital signal (dual code signal) that entered the latch circuit 5 during the second operation of the digital converter 4 then enters the digital compression circuit 7 and its number of bits is reduced. Now, if the input/output characteristic of the digital compression circuit 7 is to compress 13 bits into 11 bits by calculation using the broken line characteristic as shown in Fig. 3, the input signal level to S/N ratio will be as shown in Fig. 4. It becomes a characteristic. That is, when the input signal level increases, quantization is performed coarsely to reduce the number of bits. As a result, even though the quantization noise increases and the input signal level increases, the S/N remains at a certain level. The digital signal whose bit number has been reduced in the digital compression circuit 7 in this manner is sent to the output terminal 8 together with the level identification signal C from the level identification logic circuit 6.

The signal sent from this output terminal 8 is recorded on a recording medium or transmitted to the outside through a transmission circuit.
Next, the signal obtained by reproducing the recording medium or the signal obtained by receiving the transmitted signal is sent to the input terminal 9 on the reproducing side or the receiving side.

The digital signal input to this input terminal 9 is input to a digital expansion circuit 10, and the level identification signal sent together with the digital signal is input to a variable gain amplifier 12. The digital signal input to the digital expansion circuit 10 has its number of bits increased, is restored to the digital signal with the original number of bits, and is then sent to the digital-to-analog converter 1.
1, where it is converted into an analog signal. This analog signal is then input to the variable gain amplifier 12,
This variable gain amplifier 12 expands the analog compressed signal by performing an operation opposite to that of the variable gain amplifier 3 on the recording or transmitting side according to the instruction of the level identification signal C, thereby converting it into the original analog signal. The signal is obtained and output from the output terminal 13. By processing analog signals using analog compression length and digital compression/expansion in this manner, the S/N ratio for the input signal level of the apparatus as a whole becomes as shown in FIG.

In other words, when the input signal level is high, the S/N is stabilized at a certain level by digital compression/expansion that performs coarse quantization, and becomes unaffected by analog compression/expansion, resulting in large discontinuities on the characteristic line due to the expansion of the dynamic range. will no longer occur. As a result, the degree of amplification of the variable gain amplifier can be increased, and the dynamic range can be further expanded, and it is expected that the dynamic range will approach that of the human ear. As explained above, the analog signal processing device of the present invention generates a control signal for level identification of a digital signal after analog-to-digital conversion, and further utilizes this control signal during analog decompression. Playback errors can be reduced, and analog compression and expansion can expand the dynamic range.By adding digital compression and expansion to this, large fluctuations in S/N can be eliminated, resulting in an overall stable dynamic It is possible to expand the range.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the device of the present invention, FIG. 2 is a characteristic diagram of input signal level versus S/N associated with analog compression/expansion, and FIG. 3 is an input/output characteristic diagram associated with digital compression/expansion.
Figure 4 shows input signal level vs. S due to digital compression/expansion.
/N characteristic diagram, Figure 5 shows the input signal level vs. S of the entire device.
/N characteristic diagram. 1...Input terminal, 2...Sample hold amplifier,
3... Variable gain amplifier, 4... Analog-digital converter, 5... Latch circuit, 6... Lebel identification logic circuit, 7... Digital compression circuit, 8... Output terminal, 9 ...input terminal, 10...digital expansion circuit,
11...i digital/analog converter, 12...
Variable gain amplifier, 13...output terminal.

Claims (1)

[Claims] 1. Sample and hold means for sampling and holding an input analog signal; variable amplification means for inputting the output of the sample and hold means and changing the degree of amplification of the signal according to a control signal; and converting the output of the variable amplification means into a digital signal. The input analog signal is sampled and held by analog-to-digital conversion means and control means for identifying the level of the input analog signal from the output digital signal of the analog-to-digital conversion means and outputting a control signal to the variable amplification means. In a first period of the period, the variable amplification means is set to output the input signal as it is, the analog-to-digital conversion means converts it into a digital signal, and the control means identifies the level of the input analog signal and controls it. The amplification degree of the variable amplification means is changed according to the signal, and the analog-to-digital conversion means converts the input analog signal into a digital signal again during a second period of the sample-and-hold period, thereby producing an analog-compressed digital signal. the digital signal is compressed by digital compression means for reducing the number of bits of the digital signal, the digital signal is recorded on or transmitted to a recording medium together with the control signal from the control grenade, and is reproduced from the recording medium. means for digitally decompressing or receiving a digital signal; digital-to-analog converting means for converting the decompressed digital signal into an analog signal; and a control signal reproduced from or received from the recording medium. An analog signal processing device characterized in that the original analog signal is restored by expanding the analog signal using variable amplification means that changes the degree of amplification of the signal.