JPS6222491B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an FM stereo receiver, and more particularly to an FM stereo receiver having an automatic adjustment circuit for so-called separation, which is the degree of separation between left and right channel signals.

Composite signal V in FM stereo signal
(t) is expressed as V(t)=L(t)+R(t)+{L(t)−R(t)}·cosω _S t (1). Here, L(t) and R(t) are the left and right channel signals, and ω _S is the angular frequency of the subcarrier signal, which is 38 KHz/2π. The spectrum of the composite signal is as shown in Figure 1, and depending on the characteristics of the IF filter in the IF (intermediate frequency) stage of the receiver, the main signal M
For (t)=L(t)+R(t), sub-signal S
The power of (t)=L(t)-R(t) will decrease. As the bandwidth of the IF filter becomes narrower, this tendency becomes more pronounced, and the composite signal in equation (1) becomes as shown in the following equation.

V(t)=M(t)+kS(t) cosω _S t (2) It is a constant that 0<k1. Therefore, in order to optimize the separation of the stereo demodulated output, it is necessary to multiply the sub-signal S(t) by 1/k. In reality, separation is currently controlled by changing the bandwidth of the IF filter and simultaneously changing the matrix constant in the matrix circuit of the stereo demodulator to appropriately select the constant k.

Therefore, the present invention provides an FM system that can automatically adjust the separation to the best even if the detection characteristics change due to IF filter bandwidth switching, temperature drift, etc.
The purpose is to provide a stereo receiver.

The present invention will be explained in detail below using the drawings.

FIG. 2 is a block diagram showing one embodiment of the present invention. The RF output from the RF amplifier 1 is mixed with a local oscillator signal, which is the output of a VCO (voltage controlled oscillator) 2, in a mixer 3 and frequency-converted. The frequency-converted output is selectively amplified by an IF amplifier 4 having an IF filter, and then applied to an FM detector 5 where it is converted into a composite signal. An MPX (multiplex) stereo demodulator 6 is used to separate the left and right channel signal outputs from this composite signal.
is provided. The above system is equivalent to that of a conventional FM stereo receiver.

In this example, an oscillator 7 is further provided, and a frequency signal A cosω ₁ t outside the audio frequency is generated.
is generated (A is a constant). This frequency signal is applied to the signal generator 8, and the subcarrier signal cosω _S of the received signal obtained in the MPX demodulator 6 is
A composite signal V ₁ (t) expressed by the following equation is output using a signal synchronized with t.

V ₁ (t)=Bcosω ₁ t+Bcosω ₁ t·cosω _S t (3) Here, B is a constant determined by the gain of the signal generator 8 and the amplitude A of the frequency signal. That is, the signal generator 8 adds a multiplication signal of the frequency signal and the subcarrier signal to the frequency signal. Based on this signal V ₁ (t)
The oscillation frequency of VCO2 is controlled and FM modulated. Since the received RF signal is frequency-converted by the output of this VCO2, the received RF signal is also a signal V ₁
(t) will be FM modulated.

In addition, in order to detect the level of the frequency signal component cosω ₁ t included in the right channel output of the MPX demodulator 6, a multiplier 9 and an LPF (low pass filter) 1 are used.
A synchronous detector consisting of 0 is provided. Therefore, the right channel output and the frequency signal cosω ₁ t are used as inputs to the multiplier 9, and the DC output of the LPF 10 is input to the separation adjuster 11, which separates the left and right channel signals based on this DC output. The matrix constants are controlled so that the matrix constant is optimally adjusted.

Here, set the FM modulation sensitivity in VCO2 to K ₁
(rad/sec/V) and the FM detection sensitivity of the FM detector 5 is K ₂ (Vsec/rad), then the detection output V ₂ (t) of the FM detector 5 is expressed as follows.

V ₂ (t) = M (t) + ks (t) cosω _S t +C ₁ cosω ₁ t + kC ₁ cosω ₁ t・cosω _S t …(4) Here, C ₁ = ±BK ₁ K ₂ (upper local and the sign is different in the lower local),
k indicates the degree of reduction in the amplitude of the sub-signal by the IF filter.

Here, in the stereo demodulator 6, the circuit configurations of the left and right channels are generally balanced with each other, so it is often safe to assume that the separation in the left and right channels is also equal. Therefore, if the matrix constants of the matrix circuit in the demodulator 6 are also equal and are denoted by m, then the left channel output of the demodulator V _L
(t) becomes the following formula.

V _L (t)=C ₂ {M(t)+kmS(t) +C ₁ (1+km) cosω ₁ t} (5) Similarly, the right channel output V _R (t) is expressed by the following equation.

V _R (t)=C ₂ {M(t)−kmS(t) +C ₁ (1−km) cosω ₁ t} …(6) In equations (5) and (6), C ₂ is the value of the stereo demodulator 6. Shows the gain.

The synchronous detector consisting of multiplier 9 and LPF 10 is (6)
Since the purpose is to detect the level of cosω ₁ t in the right channel output V _R (t) shown by the formula,
The DC output of the LPF 10 is C ₁ C ₂ (1-km)/2. In other words, in the multiplier 9, V _R (t)×cos
Since a multiplication of ω ₁ t is performed, if only the DC component of this multiplication result is considered, it becomes C ₁ C ₂ (1−km)/2, which agrees with the above equation. Separation adjuster 11
, when this DC component is positive, that is, 1
> km, the value of m is increased and the matrix constant is changed so that km = 1, and when km >
1 and the DC component is negative, the matrix constant is changed so that m is small and km=1. That is, IF which is the value of k
The matrix circuit is controlled so that km=1 at all times in response to changes in the degree of sub-signal reduction due to changes in the filter bandwidth.

Therefore, the left and right channel outputs V _L (t), V _R
Since (t) is km=1 in equations (5) and (6), V _L (t)=2C ₂ {L(t)+C ₁ cosω ₁ t}...(7) V _R (t)=2C ₂ R(t) ...(8) Therefore, it is possible to always obtain the maximum separation. Note that in equation (7), the left channel output includes a component of the frequency signal cosω ₁ t outside the audio frequency, so it goes without saying that this can be removed by a filter or the like.

In the above, separation control is performed by synchronously detecting the frequency signal component from the right channel output, but separation control may also be performed by synchronously detecting the frequency signal component from the left channel output, but in this case, As can be seen from equation (5), the synchronous detection output is C ₁ C ₂ (1+km)/2, so
It becomes impossible to control the distance so that km=1. For that purpose, the output V ₁ (t) of the signal generator 8
If we use a signal such as V ₁ (t) = cosω ₁ t−cosω ₁ t・cosω _S t (9), that is, a subtraction signal, equation (5) becomes C ₂ {M(t) + kmS(t) + C ₁ (1-km) cos
ω ₁ t}, and the synchronous detection output due to cosω ₁ t is
C ₁ C ₂ (1-km)/2 is obtained and the objective is achieved.

In this example, we considered the circuit configuration in Figure 2 under the condition that the circuit configurations of the left and right channels in the MPX stereo demodulator are balanced with each other, but in a strict sense, the balance between both channels is determined by circuit constants, etc. It often collapses due to variations. Therefore, in order to achieve better separation adjustment, another example block of the present invention is shown in FIG. In the figure _, parts equivalent to those in _FIG . applied. It is mixed with the subcarrier signal cosω _S t from the MPX demodulator 6 to obtain a signal output V ₁ (t) expressed by the following equation.

V ₁ (t)=B(cosω ₁ t+cosω ₂ t) +B(cosω ₁ t−cosω ₂ t)cosω _S t (9) The constant B is equal to that in equation (3). That is, the signal generator 8 generates a multiplied signal of the difference signal of the two frequency signals and the subcarrier signal by adding it to the sum signal of the two frequency signals.

Therefore, the detected output V ₂ (t) of the FM detector 5 is expressed by the following equation.

V ₂ (t)=M(t)+kS(t)cosω _S t +C ₁ (cosω ₁ tcosω ₂ t)+kC ₁ (cosω ₁ t −cosω ₂ t)・cosω _S t …(10) Here, the right channel When the matrix constant that determines the separation from the left channel to the left channel is l, and the matrix constant that determines the separation from the left channel to the right channel is r, the left and right channel outputs of the MPX demodulator 6 are expressed by the following equations.

V _L (t)=C ₂ {M(t)+klS(t) +C ₁ (cosω ₁ t+cosω ₂ t) +klC ₁ (cosω ₁ t−cosω ₂ t)} …(11) V _B (t)=C ₂ {M(t)−krS(t) +C ₁ (cosω ₁ t+cosω ₂ t) −krC ₁ (cosω ₁ t−cosω ₂ t)} …(12) And the frequency signal cosω ₂ t included in this left channel output In order to detect the level C ₁ C ₂ (1-kl), a synchronous detector consisting of a multiplier 9b and an LPF 10b is provided, and a DC detection output of C ₁ C ₂ (1-kl)/2 is obtained. . Based on this DC output, a matrix constant that determines the separation from the right channel signal to the left channel signal is controlled by the separation adjuster 11b so that kl=1.

Similarly, in order to synchronously detect the component of the frequency signal cosω ₁ t by the multiplier 9a and LPF 10a, the right channel signal V _R (t) is multiplied by cosω ₁ t, and the LPF 10 multiplies C ₁ C ₂ (1 −kr)/2 is obtained. The separation regulator 11a operates based on this DC output and controls so that kr=1.

As a result, by setting kl=1 and kr=1 in equations (11) and (12), V _L (t)=2C ₂ {L(t)+C _1cps ω ₁ t}
…(13) V _R (t)=2C ₂ {R(t)+C _1cps ω ₂ t}
...(14) The maximum separation is obtained. In this case as well, C _1cps ω ₁ t, C _1cps ω
The component _2t is removed.

In this example, two frequency signals with different frequencies are used, but for simplicity, a single frequency signal is used.
Only the signal cosω ₁ t is generated by an oscillator,
For example, by shifting the phase using a 90° phase shifter,
A similar result can be obtained by using a signal of cos(ω ₁ t+π/2)=sinω ₁ t as another frequency signal.

As described above, according to the present invention, even if the bandwidth of the IF filter changes or its band characteristics change due to temperature drift, it is possible to always obtain the best separation. This has the advantage of eliminating the need for adjustment operations.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the bandwidth of an IF filter and the level of a composite signal, FIG. 2 is a block diagram of one example of the present invention, and FIG. 3 is a block diagram of another example of the present invention. Explanation of symbols of main parts, 2...VCO, 3...Mixer, 4...IF amplifier, 5...FM detector, 6...MPX demodulator, 7...Oscillator, 8...Signal generator, 9...Multiplier, 10... LPF, 11... Separation adjuster.

Claims (1)

[Claims] 1. Means for generating a frequency signal other than the audio frequency, generating a multiplication signal of the frequency signal and a signal synchronized with a subcarrier signal of the received signal, and adding the multiplication signal and the frequency signal. (or subtraction) and output means, and this addition (or subtraction)
means for FM modulating the received signal by an output; means for FM detecting the FM modulation output; stereo demodulation means for obtaining left and right channel outputs from the FM detection output; and the right (or left) channel output. means for synchronously detecting the frequency signal components included in the synchronous detection; and means for adjusting the separation of left and right channel outputs by controlling a matrix constant in the stereo demodulation means using the DC output obtained by the synchronous detection. FM stereo receiver. 2. means for generating first and second frequency signals outside the audio frequency, and generating a multiplication signal of the difference signal between the first and second frequency signals and a signal synchronized with the subcarrier signal of the received signal; means for adding and outputting the sum signal of the first and second frequency signals; means for FM modulating the received signal by the output of the addition; means for FM detecting the FM modulation output; stereo demodulation means for obtaining left and right channel outputs from the FM detection output; first synchronous detection means for synchronously detecting the second frequency signal component included in the left channel output; A second synchronous detection means for synchronously detecting one frequency signal component, and each DC output obtained by the first and second synchronous detection means are used to control the matrix constants of the stereo demodulation means to detect left and right signals, respectively. and means for adjusting separation of the right channel output.