JPH0457134B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a high frequency amplifier for a radio receiver using a bar antenna.

Conventional technology and its problems Conventionally, in frequency synthesizer type radio receivers, variable capacitance diodes (hereinafter referred to as VC diodes) are used in antenna tuning circuits and high frequency tuning circuits.
Since the required capacitance variable ranges are different for the two, the control voltage was supplied from a control voltage source different from the control voltage source for the VC diode of the local oscillation circuit. To aid in understanding the present invention, an example of such a conventional radio receiver will be described with reference to FIG.

In this FIG. 1, 1 indicates an antenna tuning circuit, and this antenna tuning circuit 1 is a bar antenna 1.
1, a capacitor 1c, and a VC diode 1d. A received signal induced by the bar antenna 1l and tuned by the antenna tuning circuit 1 is selectively amplified by the high frequency amplifier 2 and the high frequency tuning circuit 3. This high frequency tuning circuit 3 is a high frequency coil 3
1, a capacitor 3c, and a VC diode 3d. Reference numeral 4 denotes a mixer, to which the received signal selected by the high frequency tuning circuit 3 and the local oscillation signal from the local oscillator 5 are supplied. 6 shows a resonant circuit of the local oscillator 5, and this resonant circuit 6 includes an oscillation coil 6l, a capacitor 6c and
It is composed of a VC diode 6d. Reference numeral 7 indicates a variable frequency divider, and the frequency division ratio 1/N of this variable frequency divider 7 changes according to the desired reception frequency by a channel selection operation. The local oscillation signal from the local oscillator 5 is frequency-divided by 1/N by the variable frequency divider 7 and supplied to the phase comparator 8, where the phase is compared with the reference signal from the reference signal generator 9. 10 indicates a low-pass filter, and the output of the phase comparator 8 is connected to the VC diode 6 of the resonant circuit 6 via the low-pass filter 10 and the resistor 6r.
d, and its capacity is controlled. In this way, the local oscillator 5 is a voltage controlled oscillator whose oscillation frequency is controlled by the output of the phase comparator 8, and the local oscillator (including the resonant circuit 6) 5,
Variable frequency divider 7, phase comparator 8 and low pass filter 1
A well-known PLL is configured from 0.

11 indicates a microprocessor, and this microprocessor 11 has a frequency division ratio of 1/N of the variable frequency divider 7.
This microprocessor 11
A digital signal corresponding to the frequency division ratio 1/N of the variable frequency divider 7 is supplied to the digital/analog converter 12 from . The analog output voltage of the digital/analog converter 12 is applied via resistors 1r and 3r.
The signal is supplied to the VC diodes 1d and 3d to control their respective capacitances, and the antenna tuning circuit 1 and the high frequency tuning circuit 3 are tuned to a desired reception frequency.

Reference numeral 13 denotes an intermediate frequency amplifier, in which the output of the mixer 4 is amplified.
It should be noted that the configuration following this intermediate frequency amplifier 13 is well known, so a description thereof will be omitted.

By the way, as mentioned above, it is basically preferable to control the antenna tuning circuit 1 and the high frequency tuning circuit 3 by a control voltage source provided separately from the control voltage source of the resonant circuit 6 of the local oscillator. However, even though the configuration is complex, there are disadvantages in that the number of parts and the number of assembly and adjustment steps including tracking of the bar antenna are large.

OBJECTS OF THE INVENTION In view of the above, an object of the present invention is to provide a high-frequency amplifier for a radio receiver that can amplify a wideband received signal with a simple configuration.

Summary of the Invention The present invention provides a field effect transistor, a first parallel resonant circuit including a bar antenna provided on the gate side of the field effect transistor, and a capacitor and a coil provided on the drain side of the field effect transistor. and a second parallel resonant circuit, the resonant frequency of the first resonant circuit is set near the upper limit frequency of the receiving frequency band, and the resonant frequency of the second resonant circuit is set near the lower limit frequency of the receiving frequency band. These are selected respectively, and a wideband received signal can be amplified with a simple configuration.

Embodiment Hereinafter, an embodiment of a high frequency amplifier for a radio receiver according to the present invention will be described with reference to FIGS. 2 and 3.

In Fig. 2, 1l is a bar antenna, 2t is a grounded source field effect transistor (hereinafter referred to as
FET). This bar antenna 1
The inductance of l is L ₁ , and its both ends are
Connect between the gate and source of FET2t. 1
4 is a first parallel resonant circuit including a bar antenna 1l
This capacitance ₁₄ is composed of the distributed capacitance of the bar antenna 1l itself, the input capacitance of the FET 2t, etc., and its value is denoted by _C1 . A resistor 15 is a damping resistor having a resistance value _R1 , and is connected in parallel to the bar antenna 1l.

3l indicates a coil, the inductance of this coil 3l is _L2 , one end of which is connected to the drain of FET2t, and the other end connected to the source of FET2t via a capacitor 16. Also coil 3
1 is provided with a tap 3l, and the output of the high frequency amplifier obtained from this tap 3l is supplied to the subsequent mixer. Reference numeral 17 indicates a capacitor, and this capacitor 17 and the coil 3l constitute a second parallel resonant circuit RK ₂ , and its capacitance is C ₂ . A resistor 18 is a damping resistor having a resistance value R ₂ and is connected in parallel to the coil 3l. 1
Reference numeral 9 indicates a power supply terminal, and a power supply voltage is supplied from this power supply terminal 19 to the drain of the FET 2t via a resistor 20 and a coil 3l. In addition, capacitor 16
and resistor 20 constitute a decoupling circuit.

The operation of the above-described high frequency amplifier of this example is as follows. By appropriately selecting the inductance L ₁ of the bar antenna 1l, the resonant frequency with the capacitance C ₁ of the resonant circuit is set to the upper limit frequency _nax of the receiving frequency band (for example, long wave to medium wave band), as shown in FIG. 3A. (for example, 1611kHz). Then, as shown in FIG. 3B, L ₂ and L ₂ are set so that the resonance frequency between the inductance L 2 of the coil 3l and the capacitance C ₂ of the capacitor 17 is slightly higher than the lower limit frequency _nio (for example, 153 kHz) of the reception frequency band. Select C ₂ appropriately. Furthermore, both damping resistors R ₁ and
By appropriately selecting _R2 , the overall frequency characteristic of the high frequency amplifier of this example becomes flat over almost the entire receiving frequency band, as shown in Figure 3C. The circuit constants of this example are as follows.

Reception frequency 153 to 1611kHz L ₁ = 800μH L ₂ = 10mH C ₁ ≒10pF C ₂ = 56pF R ₁ = 560kΩ R ₂ = 33kΩ According to the radio receiver radio frequency amplifier described above, there are Since we have adopted a staggered amplifier circuit configuration in which first and second resonant circuits with different resonant frequencies are provided, there is no need for a tuning element such as a variable capacitance diode, and therefore the control for tracking with the local oscillator resonant circuit is However, it is possible to amplify a wideband received signal. Further, by appropriately selecting the resistance value of the damping resistor of each resonant circuit, the characteristics within the reception frequency band can be made flat. Furthermore, since the first parallel resonant circuit including the bar antenna exhibits inductive impedance, combined with the use of FETs with high input impedance and low noise figure, performance comparable to conventional receivers can be obtained. .

If the frequency relationship in this example above is reversed and the resonant frequency on the bar antenna side is made closer to _nio , the frequency characteristics will not change, but the number of turns of the bar antenna will increase, the induced voltage will increase, and cross modulation will occur. However, according to the present invention, there are no such drawbacks. In addition, stability and gain can be further improved by using a cascade configuration of FETs.

Effects of the Invention As detailed above, according to the present invention, it is possible to obtain a high-frequency amplifier for a radio receiver that can amplify a wideband received signal with a simple configuration.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a conventional radio receiver, FIG. 2 is a wiring diagram showing an embodiment of the high frequency amplifier of the radio receiver according to the present invention, and FIG. 3 is a diagram for explaining the present invention. It is. 1l is bar antenna, 2t is FET, RK ₁ and
RK ₂ are each parallel resonant circuits.

Claims (1)

[Claims] 1 A field effect transistor, a first parallel resonant circuit including a bar antenna provided on the gate side of the field effect transistor, and a second parallel resonant circuit including a capacitor and a coil provided on the drain side of the field effect transistor. It has a parallel resonant circuit,
The resonant frequency of the first resonant circuit is selected near the upper limit frequency of the receiving frequency band, and the resonant frequency of the second resonant circuit is selected near the lower limit frequency of the receiving frequency band. Radio receiver high frequency amplifier.