JPH07154208A - Station detection signal generating circuit - Google Patents

Abstract

PURPOSE:To generate an accurate station detection signal by decreasing dispersion in a detection sensitivity of a broadcast station due to receivers. CONSTITUTION:A radio receiver is provided with a level detection means 10 detecting a level of an operating current of an IF amplifier 4 and a reference level generating means 11 generating a reference level for a comparator 8 depending on an output of the level detection means 10. When a gain of the IF amplifier 4 is high, the level detection means 10 detects it that an current of the IF amplifier 4 is high to increase the reference level of the reference level generating means 11. When the gain of the IF amplifier 4 is small, the level detection means 10 detects it that the operating current is small to decrease the reference level of the reference level generating means 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a station detection signal generating circuit for generating a station detection signal for stopping automatic tuning in a radio receiver.

[0002]

2. Description of the Related Art Generally, in a radio receiver having an automatic tuning function, when the radio receiver starts automatic tuning and a broadcasting station is detected, the automatic tuning is immediately stopped and the radio receiver is set to the broadcasting station. To receive. Such a radio receiver is constructed as shown in FIG. In FIG. 2, the received RF signal received by the antenna is amplified by the RF amplifier (1), and the VCO of the PLL circuit (3) is mixed in the mixer (2).
It is converted into an IF signal by the local oscillation signal generated from (3a). The IF signal is amplified by the IF amplifier (4) and then detected by the wave detector (5).

When a start signal for starting automatic tuning is applied to the control circuit (3b), the VC of the PLL circuit (3)
The frequency of the local oscillation signal of O (3a) starts to change, and the received frequency changes sequentially. Each time the reception frequency changes, the electric field strength of the received signal is detected by the electric field strength detection circuit (6) based on the output of the IF amplifier (4). The output is applied from one end of the resistor (7) to the (+) terminal of the comparator (8) and compared with the reference value of the voltage source (9) applied to the (−) terminal. When the electric field strength is larger than the reference value, the comparator (8) applies the station detection signal to the control circuit (3b),
The automatic tuning is stopped, and the radio receiver receives the broadcasting station having the electric field strength higher than the reference value. In the comparator (8), if the electric field strength is smaller than the reference value, the station detection signal is not generated, so the automatic channel selection is continued.

By the way, when integrated into an IC, the operating current supplied to the IF amplifier (4) varies due to variations in h _FE of the transistors, and the gain of the amplifier (4) also varies accordingly. When a radio receiver is configured using such an IC, even if the same broadcast station is received, the output of the IF amplifier (4) differs for each radio receiver, and there is a problem that the detection sensitivity is different. . Therefore, the resistance (7) is made variable to make the output level of the electric field strength detection circuit (6) variable, or the voltage source (9) is made variable to change the detection level of the comparator (8). Thus, attempts have been made to produce accurate station detect signals.

[0005]

However, in FIG. 2, if the adjustment of the resistor (7) or the voltage source (9) is performed using a variable element, the variable element must be externally attached when integrated into an IC. Therefore, the circuit shown in FIG. 2 is not suitable for use as an IC. Moreover, since the adjustment using the variable element is performed manually, the productivity efficiency of the radio receiver is reduced. Therefore, the circuit of FIG. 2 has a problem of cost increase due to reduction of productivity efficiency and use of the variable element.

[0006]

The present invention has been made in view of the above points, and compares an IF amplifier for amplifying an IF signal with a signal indicating the electric field strength obtained from the IF amplifier and a reference value. And a comparator for generating an output signal, and the output of the comparator is a station detection signal detection circuit that serves as station detection for stopping automatic tuning, and detects the level of the operating current that determines the gain of the IF amplifier. It is characterized by comprising level detection means and reference value generation means for generating the reference value of the comparator according to the output of the level detection means.

[0007]

According to the present invention, the output of the IF amplifier is compared with the reference value in the comparator, and the output signal is generated according to the comparison result. On the other hand, the level of the operating current of the amplifier is detected by the level detecting means, and the reference value generating means applies the reference value to the comparator according to the output of the level detecting means. In this way, even if an error occurs in the operating current that determines the gain of the amplifier, the reference value of the comparator changes according to the error, so that an accurate station detection signal can be generated at all times.

[0008]

1 is an embodiment of the present invention, in which (10) is a level detecting means for detecting the level of an operating current of an IF amplifier (4), and (11) is an output of the level detecting means (10). It is a reference value generating means for generating a reference value accordingly. For the same elements as the conventional ones, the same symbols as the conventional ones are given,
The description is omitted.

In FIG. 1, the received RF signal received by the antenna is amplified by the RF amplifier (1) and is controlled by the control circuit (3b) by the mixer (2).
The local oscillation signal of a) and the received RF signal are mixed to generate an IF signal. The IF signal is amplified by the IF amplifier (4) and then detected by the wave detector (5). The IF signal is IF
Applied from the amplifier (4) to the electric field strength detection circuit (6),
The electric field strength of the broadcasting station is detected and applied to the (+) terminal of the comparator (8). On the other hand, the operating current of the IF amplifier (4) is supplied to the level detecting means (10), and the level of the operating current is detected. After that, the reference value generating means (11) generates a reference value according to the output of the level detecting means (10) and applies it to the (-) terminal of the comparator (8). In the comparator (8), the electric field strength is compared with the reference value, and the station detection signal is applied to the PLL circuit (3) according to the comparison result.

In order to perform automatic tuning, a start signal is applied to the control circuit (3b). Since the local oscillator signal of the VCO (3a) changes, the receiving broadcast station changes sequentially, and the electric field strength of the receiving broadcast station also changes sequentially. The electric field strength is compared with a reference value by a comparator (8). When the electric field strength is smaller than the reference value, the PLL circuit (3) continues to operate and automatic tuning continues.
However, as soon as the electric field strength becomes larger than the reference value, the comparator (8) applies the station detection signal to the control circuit (3b), the frequency change of the local oscillation signal stops, and the broadcasting station of the electric field strength is stopped. To receive.

Since the gain of the amplifier is proportional to the operating current, the level detecting means (10) detects the gain of the IF amplifier (4) by detecting the level of the operating current of the IF amplifier. be able to. Further, the reference value generation means (11) decreases the reference value when the level detected by the level detection means (10) is low, and conversely increases the reference value when the level is high. That is, when the level of the IF signal is constant and the gain of the IF amplifier (4) is large, the output of the electric field strength detection circuit (6) becomes large and the reference value of the comparator (8) also becomes large. . On the other hand,
When the gain of the IF amplifier (4) is small, the output of the electric field strength detection circuit (6) is small and the reference value is also small.
Therefore, the generation level of the station detection signal with respect to the IF signal can always be made constant.

FIG. 3 shows an IF amplifier (4), a comparator (8),
A specific circuit example of the level detecting means (10) and the reference value generating means (11) is shown. The level detecting means (10) includes resistors (23) and (2) to which the current I of the current source (17) is supplied.
4) and (25), and the base has the resistors (23), (2)
Transistors (26), (27) and (28) connected to the connection point of 4) and (25), and the transistor (2
6), (27) and (28) are connected to the collectors (29), (30) and (31), and the reference generating means (11) is a resistance (34) for current-voltage conversion. is there.

In FIG. 3, the IF signal applied to the input terminal (12) is the transistor (1) of the IF amplifier (4).
The amplified IF signal applied to the base of (3) is generated from the collector of the transistor (14), and the output terminal (1
From 5) is applied to the detector at the subsequent stage. Further, since the amplified IF signal is applied to the electric field strength detection circuit (6),
The electric field strength is detected according to the magnitude of the IF signal, and the detected output is applied as a DC voltage to the base of the transistor (16) of the comparator (8).

The current I of the constant current source (17) is transmitted through the current mirror circuits (18) and (19) to the transistor (1).
The current I becomes the operating current of the IF amplifier (4) as it is supplied to the common emitters of 3) and (14). Here, the gain G of the differential amplifier including the transistors (13) and (14) is the resistance value of the resistors (20) and (21) being _RL ,
The emitter resistance of the transistors (13) and (14) is set to r
If you say _e ,

[0015]

[Equation 1]

Further, the emitter resistance r _{e changes} the operating current to I
Then,

[0017]

[Equation 2]

And the gain G is

[0019]

[Equation 3]

Since the resistance R _L is set correctly in the IC, the gain G is proportional to the operating current I from the equation. Therefore, the gain of the IF amplifier can be detected by detecting the operating current of the IF amplifier. Therefore, the current I of the constant current source (17) is supplied to the series-connected resistors (23), (24) and (25) of the level detecting means (10) via the current mirror circuit (18), and the current I Detect I level. Current I
Is supplied to the resistors (23), (24) and (25), a voltage is generated at the connection points of the resistors (23), (24) and (25), and the transistors (26) and (25) are respectively generated.
Applied to the bases of (27) and (28). The transistors (26), (27) and (28) are switching transistors, and the operations of the transistors (26), (27) and (28) are selectively turned on or off according to the magnitude of the current I. . Resistances (29), (30) and (3
At one end of 1), the voltage (V
_ref- V _BE ) is applied, so the transistor (2
6), (27) and (28), the resistance (2
A current determined by the resistance values of 9), (30) and (31) and the voltage flows through the resistors (29), (30) and (31). The current obtained by adding the currents flowing through the resistors (29), (30) and (31) is supplied to the resistor (34) via the current mirror circuit (33) and converted into a voltage. The voltage generated at one end of the resistor (34) according to the current is applied to the base of the transistor (35) of the comparator (8), and the voltage becomes the reference voltage. When the current I of the current source (17) has a correct value, the transistors (26) and (27) are turned on, so that the added current of the resistors (29) and (30) is supplied to the resistor (34) and the transistor (34) is supplied. The base voltage of 35) becomes a correct reference value. Current I of current source (17)
When is small, only the transistor (26) is turned on and the current flowing through the resistor (29) is supplied to the resistor (34), so that the base voltage of the transistor (35) becomes small. Conversely, if the current I is large, the transistors (26), (2
7) and (28) are turned on, the added current of the currents flowing through the resistors (29), (30) and (31) is supplied to the resistor (34), and the base voltage of the transistor (34) becomes high.

In the comparator (8), the transistor (1
When the base voltage of 6) is higher than the base voltage of the transistor (35), the transistor (16) is turned on, and its collector current flows through the current mirror circuit (36) to the resistor (3).
7), the transistor (38) is turned on by the voltage generated at one end of the resistor (37), and the station detection signal is generated from the output terminal (39).

In the embodiment, the elements such as resistors for detecting the level of the operating current have three stages, but the number of stages of the elements is appropriately set in consideration of the accuracy of the station detection signal generating circuit and the complexity of the circuit. , The number of stages is 5, 7, and so on.

[0023]

Therefore, according to the present invention, since the reference value of the comparator for detecting the electric field strength of a predetermined value or more changes according to the gain of the IF amplifier, there is an error in the gain of the IF amplifier for each set. Even if it exists, the station detection signal can be accurately generated regardless of the set. Further, since it is not necessary to use the variable element, it is possible to have a circuit configuration suitable for an IC, and there is no need for adjustment, so that productivity efficiency is improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram showing a conventional example.

FIG. 3 is a circuit diagram showing a main part of FIG.

[Explanation of symbols]

 (6) Electric field strength detection circuit (8) Comparator (10) Level detection means (11) Reference value generation means

Claims (2)

[Claims] 1. An IF amplifier for amplifying an IF signal, and a comparator for comparing an electric field strength obtained from the IF amplifier with a reference value to generate an output signal, the output of the comparator being In a station detection signal generating circuit that serves as a station detection signal for stopping automatic channel selection, level detection means for detecting the level of an operating current that determines the gain of the IF amplifier, and a comparator of the comparator according to the output of the level detection means. A station detection signal generating circuit, comprising: a reference value generating means for generating a reference value. 2. The level detecting means and the reference value generating means are connected in series and a connection point of a first plurality of resistors to which a current equal to the operating current is supplied and a base of the first plurality of resistors are connected. A plurality of transistors connected sequentially to each other according to the magnitude of the operating current, a second plurality of resistors connected to the collectors of the plurality of transistors, and a current flowing through the second plurality of resistors. 2. The station detection signal generating circuit according to claim 1, wherein the station detection signal generating circuit comprises a third resistor that generates a reference value at one end when an added current is supplied.