JPS60136402A - Oscillating circuit - Google Patents

Abstract

PURPOSE:To pick up an oscillation output without adverse influences upon the oscillating operation by using a differential buffer amplifier and a pair of base- grounded transistors TRs to hold well isolation from a principal part of an osicllating circuit. CONSTITUTION:Oscillation is performed by TRs 1 and 2 and a resonance circuit 14. Since bases of TRs 1 and 2 performing the oscillating operation are connected commonly to bases of TRs 25 and 26 constituting the differential buffer amplifier, the oscillation output is taken out to emitters of a pair of base-grounded TRs 31 and 32, a mixer, etc. through collectors of TRs 25 and 26. Further, the oscillation output is taken out to a PLL system from the collector of the TR31. Since TRs 25 and 31 have constitution like what is called a cascode amplifier, this device is superior in isolation.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an oscillation circuit using a differential amplifier, and in particular,
The present invention relates to an oscillation circuit suitable for use in local oscillation circuits such as television tuners and FM tuners.

[Background technology and its problems]

As a local oscillation circuit used in the tuner section of television receivers, transceivers, radio receivers, etc., the oscillation frequency is stabilized by a so-called P L,r (fuse locked loop) configuration, and the oscillation frequency is stabilized within the PLL loop. There is a known system that enables digital tuning by supplying a tuning signal to a programmable taper provided in the TV. In such a local oscillation circuit, not only the oscillation output is sent to the mixer, but also the P L L
It is also necessary to send part of the oscillation output to the system. P like this
Conventionally, the pickup output of the oscillation output for the LL is taken out by connecting a resistor or a capacitor in series from a coil loosely coupled to a coil of a resonant system of a local oscillation circuit.

If the coil is picked up using a loose couple, there will be negative effects such as a reduction in the Q value of the resonant circuit and a shift in the oscillation frequency.Furthermore, since the coil picks up from the outside, it is disadvantageous in terms of mounting area or mounting space. As the number of parts increases, the number of parts also increases, which is not desirable.

OBJECT OF THE INVENTION] In view of the conventional situation, the present invention provides an oscillation circuit that can pick up oscillation output for PLL etc. with a simple configuration and does not adversely affect the resonance system or oscillation operation. purpose.

[Summary of the invention]

That is, the oscillation circuit according to the present invention is a differential type in which a resonant circuit is connected to the collector of one transistor of a pair of transistors constituting a differential amplifier, and a signal from this collector is positively fed back to the base of the other transistor. In this oscillation circuit, a differential buffer amplifier consisting of a transistor pair whose bases are connected to each base of the transistor pair described above is provided, and the output from each collector of the transistor pair of this buffer amplifier is connected to the base-grounded transistor pair. The first oscillation output is taken out from each emitter of the transistor pair of the current-voltage conversion circuit, and the second oscillation output is taken out from one of the emitters of the transistor pair of the current-voltage conversion circuit. The feature is that the load is connected to the collector and taken out from the connection point.

〔Example〕

FIG. 1 is a circuit diagram showing an example of a local oscillation circuit of a tuner section of a television receiver as an embodiment of the oscillation circuit according to the present invention.

In FIG. 1, a voltage from a base bias voltage source circuit consisting of voltage dividing resistors 3, 4, a transistor 5, and a current source 6 is applied to each base of a pair of NPN type transistors 1 and 2 whose emitters are commonly connected. , are supplied via resistors 7 and 8, respectively.

A constant current source 9 is connected to the commonly connected emitters of the transistors 1 and 2, and the base and collector of the transistor 1 and the base of the transistor 2 are connected to a terminal 11, respectively.
, 12, 13 to the resonant circuit 3- (so-called tank circuit) 14.

Here, the main parts of the oscillator other than the resonant circuit 14 are configured, for example, inside a tuner IC (integrated circuit), and each of the terminals 11, 12, and 13 corresponds to an external connection pin of the IC.

The resonant circuit 14 has a terminal 12 connected to the collector of the transistor 1.
The main part is a parallel resonant circuit consisting of a capacitor 15 and a coil 16 connected through a terminal 12.
．． 13 are connected through a capacitor 17, and the resonant frequency component approximately determined by the parallel resonant circuit of the collector output of one transistor 1 of the transistor differential pair is positively fed back to the base of the other transistor 2. This causes oscillation to occur. Further, a capacitor 18 is connected to a terminal 111 led out from the base of the transistor 1. Furthermore, when used as a local oscillator for a television tuner, the oscillation frequency needs to change depending on the tuning frequency, and for this reason, it is necessary to connect a capacitor 4 in parallel to the capacitor 15 of the parallel resonant circuit. - A series circuit of the sensor 19 and the varicap diode 20 is connected, and a control voltage for tuning is applied to the varicap diode 20 via the terminal 21 and the resistor 22.

Next, the oscillation output from such an oscillation circuit is transmitted to a pair of transistors 25 whose emitters are commonly connected, which serves as a buffer.
．． It is taken out via 26.

That is, the bases of transistors 25 and 26, which constitute the common emitter transistor pair, are connected to the bases of transistors 1 and 2, which serve as differential amplifiers for oscillation.
A constant current source 27 is connected to the commonly connected emitters of the two. The collectors of these transistors 25 and 26 are connected to the emitters of a pair of transistors 31 and 32 that constitute the current-voltage conversion circuit 30. The bases of these transistors 31 and 32 are connected in common, and are supplied with a base bias DC voltage from a voltage dividing resistor 33 and 34, and are also grounded in an AC manner via a capacitor 35, so that a so-called base It is a grounded type. This current-voltage conversion circuit 30
is transistor 2, which serves as a buffer amplifier in the oscillation circuit.
Each collector current from 5.26 is converted into a voltage, and the voltage output from each emitter of transistor 31.32 is sent to, for example, a double-balanced modulation mixer (mixer circuit). Furthermore, a resistor 36 serving as a load is connected to the collector of the transistor 31.
From the connection point with 6, a pickup output to a PLL system buffer amplifier, etc. is taken out via a capacitor 37.

Here, the transistor 25 and the common base transistor 3
1 has a configuration similar to a so-called cascode amplifier, which has high input impedance, high output impedance, small Miller effect, and excellent isolation between the oscillation circuit and PLL type buffer amplifier, etc.
The pickup output can be taken out to the PLL system while keeping the oscillation operation stable.

Next, a television tuner circuit using the above-described oscillation circuit as a local oscillation circuit will be described with reference to FIG.

FIG. 2 is a block circuit diagram showing a schematic configuration of a frequency synthesizer type television tuner circuit.

In FIG. 2, the input terminal 41 receives R, VHF signals, so-called CATV signals, etc. ranging from several tens of MHz to several hundreds of MHz.
The human input R and F signals are sent to a mixer (so-called mixer) 43 via a buffer amplifier 42 in a tuner IC (integrated circuit) 40, and the above-mentioned configuration shown in FIG. The IF' signal from the mixer 43 is mixed with the oscillation output from the local oscillation circuit 44 having
Output terminal 4 via amplifier 45 and IF output circuit 46
Extracted from 7. Here, UHFUIF” amplifier 4
A UIF signal is output from the mixer 43 by being sent to, for example, a load resistor in the mixer 43 via the IF amplifier 45 and the IP output circuit 46, and is taken out from the output terminal 41 via the IF amplifier 45 and the IP output circuit 46.

Next, in the local oscillation circuit 44 in the tuner ICJQ,
Via the above-mentioned IC external connection terminals 11, 12゜13,
The resonant circuit (so-called tank circuit) 14 having a coil, a capacitor, etc. is connected. Local oscillation circuit 44
A part of the oscillation output is taken out from a terminal 52 via a buffer amplifier 51 as a pickup output for configuring a so-called PLL circuit. This pickup output is sent to a programmable divider 54 via a prescaler 53. The prescaler 53 divides the pickup output in advance to a frequency that can be divided by the programmable divider 54.The division ratio is fixed, whereas the programmable divider 54 divides the frequency according to the channel selection signal. The ratio changes. The output from the programmable divider 54 is sent to a phase comparator 55 where the phase is compared with a reference signal of a constant frequency. The phase-compared output is sent to the tuning control voltage generation circuit 57 via an LPF (low-pass filter) 56, and the output voltage is sent to the variable capacitance element of the resonance circuit 14, for example, the varicap diode 20 mentioned above. By this, the local oscillation frequency is controlled.

Note that the terminal 61. which is led out from the mixer 43 to the outside of the IC.
62, an LC resonance circuit 63 is connected as necessary,
The mixer 43 may have a bandpass type selection characteristic such that only the above IP signal frequency component is output.

When such a television tuner circuit is integrated and configured as a so-called tuner IC, the PL
The pickup output extraction section for L can be incorporated into the IC, resulting in an extremely simple configuration compared to a conventional pickup output extraction device using a loose couple. The isolation between the oscillation circuit and the buffer amplifier is excellent, and the oscillation operation is not adversely affected. Furthermore, as a comparative example, when considering a configuration in which a load resistor or the like is connected to the collector of the transistor 2 and the pickup output is taken out from this connection point, when a low voltage source of, for example, about 5 V is used as the power supply voltage, the transistor 2 However, according to the configuration of the present invention, the voltage is extracted from the collector of the transistor 31 whose base is grounded, so that the main part of the oscillation circuit is This prevents the VCH of transistor 2 from decreasing and provides a stable oscillation level. In particular, normal VH
When applying the present invention to a local oscillation circuit of a television tuner that enables reception over a wide band from several tens of MHz to several hundred MHz, including not only F signals but also CATV signals, Oscillation level fluctuations that tend to occur can be significantly improved, and the oscillation operation and oscillation level can be sufficiently stabilized.

It should be noted that the present invention is not limited to the above-mentioned embodiment, and can be applied to various oscillation circuits other than the local oscillation circuit for tuning, for example. Furthermore, it goes without saying that the specific configuration of the resonant circuit 14 is not limited to that shown in the drawings.

〔Effect of the invention〕

According to the oscillation circuit according to the present invention, the first oscillation output to the mixer circuit, etc., and the second oscillation for pickup to the PLL system, while maintaining good isolation with respect to the main part of the oscillation circuit. Since the output can be taken out, a stable oscillation output level can be obtained under stable operating conditions without adversely affecting the oscillation operation. Further, even when the power supply voltage is lowered to about 5V, the vCE of the transistors in the main part of the oscillation circuit does not decrease, and the oscillation level can be stabilized.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a block circuit diagram showing an example of a television tuner circuit using an oscillation circuit according to the present invention as a local oscillation circuit. 1.2, 25.26, 31.32...transistor 1
4...Resonance circuit 30...Current-voltage conversion circuit 36...
... Load resistor patent applicant Sony Corporation representative Patent attorney Kodo Koike 1) Sakae Mura -

Claims (1)

[Claims] Differential type oscillation in which a resonant circuit is connected to the collector of one transistor of a pair of I transistors constituting a differential amplifier, and a signal from this collector is positively fed back to the base of the other transistor. In the circuit, a differential buffer amplifier consisting of a pair of transistors is provided, each base of which is connected to the base of each transistor pair, and the output from each collector of the transistor pair of this buffer amplifier is connected to a base-grounded transistor pair. The first oscillation output is taken out from each emitter of the transistor pair of the current-voltage conversion circuit, and the second oscillation output is sent to the current-voltage conversion circuit. An oscillation circuit characterized in that a load is connected to the collector of one of a pair of transistors of a voltage conversion circuit, and the load is extracted from the connection point.