JP2676756B2 - Receiver front end - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a front end using a printed coil of a receiver.
It's about the end.

2. Description of the Related Art In recent years, a print coil using printed wiring has been adopted in a tuning circuit at the front end of a receiver.

An example of the front end of the above-described conventional receiver will be described below with reference to the drawings.

FIG. 2 shows a block diagram of the front end of a conventional receiver. In FIG. 2, 1 is an antenna input, 2 is a receiving frequency tuning circuit composed of a print coil L1, a variable capacitance diode C _D1 and an additional capacitance (trimmer capacitor) C ₁ , 3 is a print coil L2 and a variable capacitance diode C _D2 And an oscillation frequency tuning circuit composed of an additional capacitance C ₂ .
4 is the reception frequency ₁ and, as a result, the upper oscillation frequency ₂
The intermediate frequency ₃ of 5 is output by the mixing circuit of. Therefore, there is a relationship of ₂ = ₁ + ₃ .

The capacitance characteristic obtained by the tuning voltage V _T applied to the variable capacitance diode is shown in FIG. 3a. The frequency of the tuning circuit is As a result, the tuning voltage versus frequency changes as shown in Figure 3b. Then, the tuning voltage is varied from V _{Tmin to} V _Tmax to cover the reception frequency band. At this time, the difference between the receiving frequency ₁ and the oscillating frequency ₂ must always be a constant intermediate frequency ₃ for optimum tuning. Therefore, the variable-capacitance diodes C _D1 and C _D2 are divided into ranks and parts with uniform characteristics are used. Then, the coil and the additional capacitance are adjusted to match the tracking. Here, a print coil of printed wiring is used as the coil, and even if the L value varies due to etching of the printed wiring board, the printed coils L1 and L2
Since there is no adverse effect on the tracking because the L value of is changed to the same ratio, the L value is set in advance by a copper foil pattern so that the tracking is designed by design. Then, the tracking is adjusted by the additional capacitances C ₁ and C ₂ , but if the oscillation frequency ₂ is controlled by the PLL frequency synthesizer circuit 6, the adjustment point for tracking adjustment is the additional capacitance C ₁ (≈ It is only a 7pF trimmer capacitor). If the number of stages of the reception frequency tuning circuit increases, a trimmer capacitor will be added and adjusted accordingly.

SUMMARY OF THE INVENTION However, the above-described configuration has a problem that it is difficult to rationalize the manufacturing process because the adjusting component and the adjusting process are required.

In view of the above problems, the present invention provides a front end of a receiver that eliminates tracking adjustment in the manufacturing process.

Means for Solving the Problems In order to solve the above problems, the receiver front end of the present invention eliminates the additional capacitance of the reception frequency tuning circuit, and includes a tuning circuit consisting of a printed coil by printed wiring and a variable capacitance diode. The oscillation frequency tuning circuit and the receiving frequency equivalent circuit are provided in all stages, and the coupling capacitance between the oscillation frequency tuning circuit and the oscillation circuit semiconductor element and the additional capacitance provided in the oscillation frequency tuning circuit are used as fixed capacitors for tracking correction. Is.

Operation The present invention can streamline the manufacturing process by reducing the factor that takes a while to eliminate the adjustment part by the above-mentioned configuration.

Embodiment A receiver front end according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a front end of a receiver according to an embodiment of the present invention. The description of the parts in FIG. 1 given the same numbers as in FIG. 2 is omitted. 12 is a printed coil
Reception frequency tuning circuit composed of L11 and back-to-back variable capacitance diode C _D11 , 13 is printed coil L12
And the back-to-back type variable capacitance diode C _D12 , the equivalent capacitance C'as seen from the base side of the oscillation transistor, and the coupling capacitance C
And an oscillation frequency tuning circuit composed of a combined capacitance C12 of an additional capacitance C2 '. Local oscillation frequency ₂ is reception frequency ₁
Only the intermediate frequency of ₃ (10.7MHz) above
₁ is a so-called FM American band of 87.5 MHz to 108 MHz, and is controlled by the PLL frequency synthesizer circuit 6 as in the conventional example. The back-to-back type variable capacitance diodes C _D11 and C _D12 are ranked and selected to have the same characteristics and placed as C _D11 = C _D12 = C _D, and C _Dmin = 33 pF is selected as the capacitance value at the lower limit of the band for tracking. When you get From each formula of L11 = 0.1μH, C _Dmax = 21.7pF, L12 = 0.073
μH, C12 = 2.8pF is required. Actually, the value is slightly different due to stray capacitance and coupling between circuits. By mounting components, the coupling capacitance C value is 6pF and the additional capacitance C2 'is 0.5pF so that the oscillation circuit oscillates stably. Select and print coil L1
L value of 1, L12 and tuning voltage V _T applied to the variable capacitance diode
Set while tracking.

When the tuning circuit is designed as described above, the factors that cause tracking deviation are that the print coils L11 and L12 have a slight variation in their values due to etching, environmental conditions, etc. As long as they are composed of the same printed wiring board, they will change at the same ratio, so tracking will not be adversely affected.
There is a variation of 2. However, if a component having a small deviation such as ± 0.25 pF is used as the coupling capacitance C, the value of the combined capacitance C12 is small, so that the variation of the entire tuning capacitance is small. Therefore, since the influence on tracking is small, the coupling capacitance C may be a fixed capacitor.

Further, as in the conventional example, the one-element type variable capacitance diode requires the coupling capacitance Co in series, but when the back-to-back type variable capacitance diode is used as in this embodiment, the coupling capacitance Co
Since there is no need for components, there are fewer elements that vary due to fewer parts.

Further, in the present embodiment, in order to reduce the influence on the tracking of the coupling between the circuits, the printed coils are provided with taps to connect the circuits.

As described above, according to this embodiment, the tuning circuit including the print coil and the variable capacitance diode is provided in all stages of the oscillation frequency tuning circuit and the receiving frequency tuning circuit, and the coupling capacitance between the oscillation frequency tuning circuit and the oscillation circuit semiconductor element is provided. Since C and the additional capacitance C2 'provided in the oscillation frequency tuning circuit are used as the capacitors for tracking correction, the coupling capacitance C may be a fixed capacitor, so that parts requiring adjustment can be eliminated.

In the claims, the upper limit of the oscillation frequency is
When the reception frequency is on the upper side, the capacitance change ratio of the tuning capacitance from min to max must be smaller in the reception frequency tuning circuit, so the reception frequency tuning circuit requires additional capacitance (about 5 pF) for tracking correction, This is because there are more factors that cause variations. However, if the reception sensitivity may vary, the oscillation frequency is controlled by the PLL frequency synthesizer circuit, so this additional capacitance may be a fixed capacitor.

As described above, according to the present invention, the tuning circuit including the print coil and the variable capacitance diode is provided in all stages of the oscillation frequency tuning circuit and the reception frequency tuning circuit, and the oscillation frequency tuning circuit is coupled to the oscillation circuit semiconductor element. Since the capacitance and the additional capacitance provided in the oscillation frequency tuning circuit are used for tracking correction capacitors, adjustment parts can be eliminated, the cost of components can be reduced, and the manufacturing process can be rationalized without the need for adjustment processes. It has extremely high industrial utility value.

[Brief description of the drawings]

1 is a block diagram of a front end of a receiver according to an embodiment of the present invention, FIG. 2 is a block diagram of a front end of a conventional receiver, and FIG. 3a is a characteristic diagram of a variable capacitance diode. FIG. 3b is a tuning voltage vs. frequency characteristic diagram. 12 …… Reception frequency tuning circuit, 13 …… Oscillation frequency tuning circuit, L11, L12 …… Print coil, C _D11 , C _D12 …… Variable capacitance diode, C …… Coupling capacitance.

Claims (1)

(57) [Claims] 1. A tuning circuit having an oscillation frequency above the reception frequency and comprising a printed coil formed by printed wiring and a variable capacitance diode is provided in all stages of the transmission frequency tuning circuit and the reception frequency tuning circuit, and the oscillation frequency tuning is performed. A receiver front end, characterized in that a coupling capacitor with an oscillation circuit semiconductor element of the circuit and an additional capacitor provided in an oscillation frequency tuning circuit are fixed capacitors for tracking correction.