KR940011031B1 - Rf band switching circuit - Google Patents

Abstract

The RF band switching circuit is constructed that an RF signal from a first RF switching diode is amplified at a first RF amplifying transistor, an RF signal from a second RF switching diode is amplified at a second amplifying transistor, the RF signals amplified at the first and second RF amplifying transistors are supplied to a mixer, band selection voltage signals are applied to the bases of the first and second RF amplifying transistors, the first and second RF switching diodes are biased to a voltage appearing at the emitter output voltage of the first and second RF transistors, thereby reducing power consumption of the circuit.

Description

RF band switching circuit

1 is a conventional RF band switch circuit diagram.

2 is an RF band switch circuit diagram of the present invention.

* Explanation of symbols for main parts of the drawings

F ₁ : VHF Band Pass Filter F ₂ : UHF Band Pass Filter

Q ₁₁ , Q ₁₂ : RF amplifying transistors D ₁₁ , D ₁₂ : RF switching diode

C ₁₁ , C ₂₂ : capacitor R ₁₁ -R ₂₀ : resistance

L ₁₁ -L ₁₄ : Coil

The present invention relates to an RF band selection circuit of a double conversion tuner, and more particularly, to an RF band switching circuit capable of minimizing matching loss when selecting a VHF band / UHF band using a bias of an RF amplifier. The RF stage of the double conversion tuner includes a VHF / UHF RF filter for filtering the RF input signal for each band and an RF amplifier for amplifying and passing the signal passed through the RF filter to the mixer.

A conventional embodiment of an RF stage for such band switching is shown in FIG. As referred to herein, the RF input signal includes a first signal path consisting of an RF switching diode (D ₁ ) -VHF band pass filter (F ₁ ) -RF switching diode (D ₄ ) and an RF switching diode (D ₅ ). The RF amplifier A ₁ is configured to be commonly input to the RF amplifier A ₁ via a second signal path including the UHF band pass filter F ₂ and the RF switching diode D ₈ . The signal is configured to be provided to a mixer (not shown).

The first signal path is a VHF signal path and the second signal path is a UHF signal path, and an RF switching diode (D ₂ ) and a capacitor (C ₁ ) are respectively across the VHF band pass filter (F ₁ ) on the first signal path. A series circuit and an RF switching diode (D ₃ ) and a series circuit of the capacitor (C ₂ ) are provided, and the RF switching diode (D ₆ ) and the capacitor are respectively across the UHF band pass filter (F ₂ ) on the second signal path. A series circuit of (C ₃ ) and a series circuit of an RF switching diode D ₇ and a capacitor C ₄ are provided.

Meanwhile, before and after the first and second signal paths, a B + voltage for turning on the RF switching diodes D ₁ , D ₅ -D ₆ , and D ₈ is applied, respectively, and the RF switching diodes D ₂ , _{D 3), (D 6,} D 7) , the respective switching transistor (Q ₁₎ (Q configuration ₂₎ B + voltage is to be applied through, and the RF switching transistors (Q _1, Q ₂₎ each of the PLL circuit UHF / VHF band selection voltage signal (S ₁ , S ₂ ) is configured to be controlled.

Here the resistors R ₁ -R ₈ are for bias.

In such a circuit, for example, when the UHF / VHF band selection signals S ₁ and S ₂ are high and low, respectively, the switching transistors Q ₁ and Q ₂ are turned off and on, respectively.

Therefore, the RF switching diodes D ₆ and D ₇ are turned on to bypass the UHF RF signal to ground through the capacitors C ₃ and C _{4 at} the front and rear ends of the UHF band pass filter F ₂ . The VHF RF signal through the (D ₁ ), the VHF band pass filter (F ₁ ), and the RF switching diode (D ₄ ) is applied to the mixer through the RF amplifier (A ₁ ).

On the contrary, when the previous UHF / VHF band selection voltage signals S ₁ and S ₂ are low and high, respectively, the switching transistors Q ₁ and Q ₂ are turned on and off, respectively. Therefore, the B + voltage at the collector terminal of the switching transistor Q ₁ forward biases the RF switching diodes D ₂ and D ₃ through the resistor R ₂ , so that the VHF RF signal on the first signal VHF path is VHF. At the front and rear ends of the band pass filter F ₁ , each of the RF switching diodes D ₂ and D ₃ is bypassed to ground through a series circuit of the capacitors C ₁ and C ₂ . The UHF RF signal passing through the RF switching diode D ₅ and the RF switching diode D ₈ of the UHF bandpass filter F ₂ is amplified by the RF amplifier A ₁ and applied to the mixer.

However, this conventional RF band switching circuit uses a large number of (8) RF switching diodes and also amplifies the current to amplify the band select signal from the PLL IC to secure the driving current required to drive these RF switching diodes. Since the transistor is required, it leads to complicated circuit configuration and excessive power consumption.

In particular, in the conventional circuit, when one RF band is selected, the signal path of the other band cannot be completely blocked, and thus there is a problem in that an unnecessary signal is incorporated into the selection signal or the influence of mutual interference cannot be excluded.

The present invention proposes an RF band switching circuit capable of improving the noise figure characteristic by simplifying the circuit configuration and minimizing the matching loss. Hereinafter, the present invention will be described with reference to the accompanying drawings.

2 is a circuit diagram of the present invention, the RF input signal via the RF switching diode (D ₁₁ ) is connected to be input to the base of the first RF amplifier transistor (Q ₁₁ ) through the VHF band pass filter (F ₁ ), The RF input signal passing through the RF switching diode D ₁₂ is connected to the base of the second RF amplifying transistor Q ₁₂ through the UHF band pass filter F ₂ .

In addition, the band selection voltage signal S of the PLL IC (not shown) is provided at the base of the first and second RF amplifier transistors Q ₁₁ and Q ₁₂ through respective resistors R ₁₄ and R ₁₅ (R ₁₉ and R ₂₀ ). ₁ and S ₂ are connected so as to be applied with a bias voltage, and each emitter output of the first and second RF amplifying transistors Q ₁₁ and Q _{12 is} connected to the coil L ₁₂ and the resistors R ₁₁ and R ₁₂ . A coil L ₁₄ and a resistor R ₁₆ , R _{17 are} connected to each RF switching diode D ₁₁ , D ₁₂ so as to be provided as a bias.

The collector outputs of the first and second RF amplifier transistors Q ₁₁ and Q _{12 are} connected to each other through a coupling capacitor C ₁₄ and C ₂₀ to be provided to a mixer (not shown). The collectors of the first and second RF amplifying transistors Q ₁₁ and Q ₁₂ are connected to the B + voltage through the power supply noise absorbing coils L ₁₁ and L ₁₃ and the capacitors C ₁₆ and C _22, respectively.

In the figure, capacitors C ₁₁ -C ₁₃ and C ₁₇ -C ₁₉ are for coupling, capacitors C ₁₅ and C ₂₁ are for bypass, and resistors R ₁₃ and R ₁₉ are emitter output resistors.

Referring to the operation and effects of the present invention configured as described above are as follows.

In FIG. 2, when the band select voltage signals S ₁ and S ₂ are high and low, respectively, the first RF amplifying transistor Q ₁₁ is base biased with a voltage signal through the resistors R ₁₄ and R ₁₅ . And the second RF amplifier transistor Q ₁₂ is turned off. Therefore the claim 2 RF amplifier transistor (Q ₁₁₎ the emitter output resistance (R _13), the B + voltage is displayed and the RF switching by the emitter output voltage diode (D ₁₁₎ is so turned on, coupling capacitor (C ₁₁ The RF input signal passing through the) -RF switching diode (D ₁₁ ) -coupling capacitor (C ₁₂ ) passes through the VHF band pass filter (F ₁ ) and is amplified by the first RF amplifier transistor (Q ₁₁ ) and output to the mixer. .

At this time, since the RF input signal is not transmitted to the UHF band pass filter F ₂ and the second RF amplification transistor Q ₁₂ is also turned off, any signal is output from the collector stage of the second RF amplifying transistor Q ₁₂ . Will not be.

Conversely, if the band select voltage signals S ₁ , S ₂ are low and high, respectively, this time the second RF amplifying transistor Q ₁₂ is turned on by the bias voltage signal through the resistors R ₁₉ , R ₂₀ , At this time, the first RF amplifier transistor Q ₁₁ is turned off.

Therefore, the voltage B + shown on the emitter output resistance R _{18 of} the second RF amplifier transistor Q ₁₂ turns on the RF switching diode D ₁₂ while passing through the coil 14 and the bias resistors R ₁₆ and R ₁₇ . Let's go.

Eventually, it is amplified in the second RF amplifying transistor Q ₁₂ via an RF band pass filter F ₂ through the coupling capacitor C ₁₇ -RF switching diode D ₁₂ -coupling capacitor C ₁₈ . The RF signal of the UHF band is transmitted to the.

Similarly, in this case, since the first RF amplifying transistor Q ₁₁ is off, there is no collector output.

That is, according to the present invention, the switching diode D ₁₂ of the UHF band signal path and the amplifying transistor Q ₁₂ and the switching diode of the VHF band signal path according to the logic of the UHF / VHF band selection voltage signals S ₁ and S ₂ By selectively switching D ₁₁ ) and amplifying transistor Q ₁₁ , power consumption for circuit configuration can be reduced and noise figure can be improved by minimizing matching loss.

In particular, the present invention allows the tuner set size to be reduced and the cost can be reduced by simplifying the band switching circuit configuration.

Claims (1)

The RF input signal passing through the RF switching diode D ₁₁ is configured to be amplified by the first RF amplification transistor Q _{11 to} which the B-voltage is applied to the collector through the VHF band pass filter F ₁ , and the RF switching diode ( The RF input signal passing through D ₁₂ is configured to be amplified by the second RF amplifying transistor Q _{12 to} which the B + voltage is applied to the collector through the UHF band pass filter F ₂ , and the first and second RF amplifying transistors ( RF signals amplified by Q ₁₁ and Q ₁₂ are configured to be provided to a mixer in common, and resistors R ₁₄ , R ₁₅ , and () at the bases of the first and second RF amplifying transistors Q ₁₁ and Q ₁₂ , respectively ( The band select voltage signals S ₁ and S ₂ through R ₁₉ and R ₂₀ are applied, and the RF switching diodes D ₁₁ and D ₁₂ are first and second RF amplifying transistors Q ₁₁ and Q, respectively. RF band, characterized in that configured to be biased in the B + voltage that appears in each of the emitter output resistance (R _13, R _{18) 12)} Switching circuit.