JPH0783287B2 - High frequency amplifier - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high frequency amplifier used for a television receiver or the like.

2. Description of the Related Art In recent years, with the development of new media equipment, high-frequency amplifiers have been required to have better performance than ever before.

An example of the above-described conventional high frequency amplifier will be described below with reference to the drawings.

FIG. 5 is a block diagram showing a configuration of a conventional high frequency amplifier, and FIG. 6 is a circuit diagram showing a concrete example thereof. In FIG. 5, 51 is a high frequency amplifier, 52 is a mixer circuit, and terminals are
5A is an input terminal, 5B is an input terminal for inputting a local oscillation signal, and 5C
Is the IF output terminal.

In the high-frequency amplifier configured as described above, the input signal is supplied from the input terminal 5A to the high-frequency amplifier 51, amplified, and then frequency-converted by the mixer circuit 52 to generate a signal of the first intermediate frequency (hereinafter referred to as IF signal). Write) is supplied to the next stage as an output from terminal IF output terminal 5C. Since the IF signal is set above the input band (90 MHz to 770 MHz) (for example, 950 MHz band), the local oscillation signal is supplied to the mixer circuit 52 from the input terminal 5B as a frequency higher by the input signal IF.

FIG. 6 shows a concrete circuit configuration diagram of the present apparatus thus configured as described above. In Figure 6, 61,610,611,612,613 are FE
T-transistors, 62,66,616,619 are coupling capacitors, 68,6
17,614 is a balun transformer, 64,615,618 is a bias potential,
63 is a bias resistor, 65 is a choke coil, each terminal is 6A
Is an input terminal, 6B is a power terminal, 6C is an output terminal, and 6D is an input terminal for inputting a local oscillation signal. The operation of this configuration will be described above.

First, the input signal is supplied from the input terminal 6A, is supplied to the amplifying transistor 67 via the coupling capacitor 62, is amplified here, and is supplied from the drain of the FET transistor 61 to the balun transformer 68 via the coupling capacitor 66. , Where unbalanced-balanced conversion is performed and FET transistors 610, 611, 6
It is supplied to two common sources of a mixer circuit in which four of 12,613 are double-balanced. The local oscillation signal is supplied to the two common gates of the four FET transistors from the input terminal 6D through the balun transformer 614 that performs the unbalanced-balanced conversion, and the two common drains of the four FET transistors have two signal frequencies. The sum and difference components are output. The balun transformer 617 performs balanced-unbalanced conversion, and supplies the IF bandpass filter stage from the output terminal 6C via the coupling capacitor 619.

Problems to be Solved by the Invention However, the above configuration has a drawback that it causes IF interference when there is an IF band signal in the input stage, and the impedance seen from the input side of the balun transformer 68 is that of the FET. There is a drawback that the input capacitance makes it capacitive, and the capacitance value deteriorates the gain at the upper limit of the reception band (700 to 770 MHz).

In view of the above problems, the present invention attenuates the signal in the IF band before the mixer stage, and the upper limit of the reception band (700 MHz ~
(770 MHz) to provide a high-frequency amplifier device that simultaneously satisfies the compensation for gain deterioration at 770 MHz.

Means for Solving the Problems In order to solve the above problems, the high-frequency amplification device of the present invention, after high-frequency amplification of the input signal, becomes a trap for IF and causes peaking around 700 to 770 MHz. After passing through a filter circuit, it is then supplied to a mixer circuit consisting of a double-balanced FET structure for frequency conversion.

Effect The present invention can solve the IF interference by inserting a filter circuit that becomes a trap structure for IF and becomes peaking for 700 MHz to 770 MHz by the above-described configuration, and per the upper limit of the reception band. It is possible to prevent the gain deterioration in.

Example A high frequency amplifier according to an example of the present invention will be described below with reference to the drawings. FIG. 2 is a block diagram showing the configuration of the high frequency amplifying apparatus in one embodiment of the present invention. In FIG. 2, 11 is a high frequency amplifier, 12 is a filter circuit,
13 is a mixer circuit, 1A is an input terminal, 1B is an input terminal for inputting a local oscillation signal, and 1C is an output terminal.

The operation of the high frequency amplifier configured as above will be described below. First, the input signal is the high frequency amplifier 11
After passing through, it enters the filter circuit 12. Here, the filter circuit 12 is configured to be a trap for the IF and a peaking circuit for compensating the input capacitance of the mixer circuit 13 at the high end of the reception band. The output is the mixer circuit 13
Is converted to IF at and is supplied to the IF band pass filter from output terminal 1C.

FIG. 1 shows a concrete circuit configuration example of the embodiment of FIG. In Fig. 1, 21,213,214,215,216 are FE
T transistors, 22, 26, 219 and 222 indicate coupling capacitors, and 24, 212, 218 and 221 indicate bias potentials. Reference numeral 25 is a choke coil, 210, 217 and 220 are balance transformers, 23 is a bias resistor, 29 is an input conversion capacity of the mixer stage, so-called stray capacitance, 27 is a resonance coil, 28 is a resonance capacitor, 2A is an input terminal, 2B is a power supply terminal, 2C is an IF output terminal, and 2D is an input terminal for inputting a local oscillation signal.

The operation of this embodiment having the above configuration will be described. First, the input signal is given to the gate of the FET transistor 21 from the terminal 2A via the coupling capacitor 22, and is amplified here. The amplified signal is supplied from the drain of the FET transistor 21 via the coupling capacitor 26 to the filter circuit 12 configured as a coil 27, a resonance capacitor 28, and a stray capacitance 29.
As shown in FIG. 3, the characteristic of this filter circuit is an anti-resonance point at the frequency ₀₁ corresponding to IF, and the reception band 700 to 7
At a frequency corresponding to ₀₂ corresponding to the 70 MHz band, a peaking circuit of series resonance is obtained. This characteristic is as shown in FIG. 4, and in the area ₀₂ , the gain deterioration in the conventional example is peaked and compensated. This output is given via a balun transformer 210 to the common source of the mixer circuit obtained by double-balancing the four FET transistors 213, 214, 215, 216, and the local oscillation input signal obtained from the input terminal 2D is balun transformer to the common gate. In addition, the signal of the sum and difference of the two signals generated in the common drain is supplied from the terminal 2C to the IF band pass filter stage via the balun transformer 220 and the coupling capacitor 222. Balun transformer
Optimal biases are applied to 217, 210, 220 by bias potentials 212, 218, 221 respectively.

As described above, according to the present embodiment, after the input signal is passed through the high frequency amplifying transistor 21, the input capacitance of the mixer circuit is used to cause a trap for IF and peaking for 700 to 770 MHz. By constructing a filter circuit and applying it to it, the IF can be attenuated and the gain deterioration around the upper limit of the reception band (700 to 770 MHz) can be improved.

As described above, according to the present invention, after amplifying the input signal by the high frequency amplifying transistor of the FET, the coil, the capacitance, and the input source capacitance of the FET mixer are made to resonate in parallel and the filter circuit is configured. By supplying and trapping for IF and peaking for the 700 to 770 MHz band of the reception band, it is improved by IF interference and 700
The gain in the ~ 770MHz band can be improved.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a high frequency amplifier in one embodiment of the present invention, FIG. 2 is a block diagram showing the basic configuration of FIG. 1, and FIG. 3 is an impedance characteristic diagram of the filter circuit of FIG.
FIG. 4 is a characteristic diagram showing the pass characteristic of FIG. 3, FIG. 5 is a block diagram showing a configuration of a conventional example, and FIG. 6 is a circuit diagram showing a concrete circuit configuration example of FIG. 11 …… High frequency amplifier, 12 …… Filter circuit, 13 …… Mixer circuit, 21 …… FET transistor, 27 …… Resonance coil, 28 …… Resonance capacitor, 29 …… Stray capacitance.

Claims (1)

[Claims] 1. A high-frequency amplifier for amplifying an input signal, a parallel resonance circuit including a coil and a capacitor inserted on the output side of the high-frequency amplifier, and a mixer circuit having a double-balanced structure with four FET transistors, The two common sources of this mixer circuit are impedance-converted by a balanced-unbalanced balun, and a series-parallel resonant circuit is configured by the equivalent capacitance seen from the unbalanced side of the balun and the parallel resonant circuit described above. Set the resonance point to 950MHz band
Set to 700 to 770MHz band, apply local oscillation input signal from two common gates of the above double balance mixer circuit, change two common drains to unbalance by balun, and then select intermediate frequency of 950MHz band. A high-frequency amplifier characterized by being used as a product.