JPS6318195Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a receiver in which a high frequency amplifier is provided with a gain adjuster, and this is varied during manufacturing, thereby making it possible to adjust receiving sensitivity and intermodulation distortion to optimal values.

BACKGROUND ART Conventionally, in receivers for mobile communication radio devices, reception sensitivity and cross-modulation characteristics due to two-signal input are specified by the Radio Law. However, since these two characteristics are contradictory to each other, non-standard items occur during receiver adjustment during mass production, which is a hindrance to assembly work.
For this reason, a high-level engineer is required to make this adjustment, but this involves work such as replacing transistors and changing circuit component constants, which is a bottleneck during mass production.

In the case of FM modulation, a single superheterodyne receiver used for mobile communications is a block diagram as shown in Figure 1.

In FIG. 1, 1 is the input terminal of the received signal to which the output of the duplexer of the radio or the antenna is connected;
2 is an RF amplifier RFA, 4 and 12 are band filters
BPF, 10 is converter CONV, 11 is local oscillator, 13 is intermediate frequency amplifier IFA, 14 is disk drive DSK, 15 is noise squelch NoiseSQ, 1
6 is a standard FM receiver consisting of a low frequency amplifier, and demodulated audio output is output from an output terminal 17.

Generally, the service radius of one zone for a car phone that uses several hundred channels is about 10 km, and when a mobile station approaches a base station, it is several tens of meters away, so the receiver input has a low level threshold of about -120 dBm. Due to the strong input of -30 dBm from the input, the fluctuation range of the receiving input is approximately 90 dB. There are 10 base stations
Since multiple radio waves are emitted simultaneously, if the reception input is strong, odd-order cross modulation causes a problem of cross modulation distortion in which signals that are not originally transmitted by the base station are generated within the receiver. In other words, there is a seesaw-like relationship in which increasing the receiver sensitivity degrades the cross-modulation characteristics, and decreasing cross-modulation distortion degrades the receiving sensitivity, and these relationships have reached a state where there is not much leeway between them. There is.

However, as a result of various studies, it has been found that intermodulation distortion and receiving sensitivity are subtly related to the gain from the receiving input to the frequency converter. Conventionally, this gain adjustment involves changing the constants of the tuning circuit or transistor amplifier, but this requires the installation and removal of parts in order to meet the specified standards, which requires a large number of adjustment steps and a considerable amount of time, so it is not suitable for high-end products. There are cases where a large number of engineers are assigned to maintain a mass production system, so some kind of countermeasure was needed.

In order to eliminate these drawbacks, the present invention inserts a gain adjustment section between the stages of the high-frequency amplifier to cancel the variation in gain due to variation in the parts used, thereby reducing costs by shortening the adjustment time and homogenizing the product characteristics. The purpose is to achieve this goal.

This will be explained below along with examples.

FIG. 2 shows the detailed configuration from the high frequency amplifier to the frequency conversion section, which is the main part. 1st
The RF amplifier 2 corresponding to block 2 in the figure consists of a first stage high frequency amplifier 2a and a second stage high frequency amplifier 2b, which are connected in tandem. 4 is a bandpass filter for removing adjacent signals, 5 is its output terminal, and 6 is a power supply terminal.

Since the high frequency amplifier first stage amplifier 2a is an ordinary amplifier as shown in the figure, a detailed explanation thereof will be omitted. The second stage amplifier 3 is a variable amplifier that is the main part of this embodiment.

31 is a coupling capacitor with the first stage amplifier 2;
32 is a transistor, 35 is a series resistor, 33 is a variable resistor, 34 is a bypass capacitor, 36,3
7 is a voltage divider element that supplies the bias voltage of the transistor 35; 38 and 39 are the transistors 35;
self-bias circuit, 40 is a transistor 35
The variable inductance on the collector side forms a tuned circuit together with the collector capacitor. 41,
42 is a CR type decoupling filter, 43 is a coupling capacitor with the next stage band filter 4, 5
is the same output terminal, and 6 is a power supply connection terminal.

Next, the operation of this circuit will be explained. variable resistance 33
When it is turned to the a side, the series resistor 32 is shot, and the output of the previous stage 2a is inputted to the transistor 35 without loss. When the variable resistor 33 is turned to the b side, the series resistor 32 and the variable resistor 33 are connected in parallel, and are connected to the midpoint of the voltage dividers 36 and 37, forming a CR low-pass filter for the bypass capacitor 34.
The input to transistor 35 is reduced. This adjustment provides a 10-15dB reduction at 150MHz.

Next, the relative relationship between the change in reception sensitivity and the intermodulation distortion IM when the gain of the high frequency amplifier is changed will be explained.

Figure 3 shows the gain change of the variable gain amplifier as the attenuation amount.
For dB, 1 receiver total NF on the left,
The receive input that produces 2.20dBQS is shown on the IM on the right.
That is, NF changes upward to the right, and IM changes downward to the right, with opposite characteristics. NF ₁ when the attenuation is OdB
= 6dB, IM = 65dB receiver, the said amplifier
When attenuating by 10dB, NF = 12.5dB and IM = 75dB.

Currently, the standard values of IM and NF are IM=68dB,
When NF=10 dB, the allowable attenuation amount is 3 dB or more for IM as shown by arrow B, and 7.5 dB or less for NF as shown by arrow A. Therefore, the adjustment range is 4.5dB. At this time, the amount of attenuation at the fusion point between the two is approximately 5 dB.

Next, when the receiver NF is improved to 3 dB by improving the NF after the frequency converter, IM = 68 dB, NF
The attenuation that satisfies =10dB is 3dB for IM and 3dB for NF.
It becomes 10.5dB and the adjustment range expands to 7.5dB. It can be seen that the fusion point I' between the two is about 6.5 dB.

Currently, in standards that emphasize NF, the attenuation is set to 0 dB, NF3dB, IM = 65dB, and when IM is emphasized, the attenuation is set to 10.5dB, IM is 75dB, NF is 10dB.
You can adjust it so that

NF and IM characteristics are specified individually depending on the communication method that uses them, but the IM standards are loose and
If NF is important, set the attenuation to 0 dB and maximize the gain of the high frequency amplification section.If the IM standard is strict and the NF standard is easy, set the attenuation to 10.5 dB and the IM will be
75.5dB, NF is 10dB. In this way, by using the same model, one that satisfies the target standard can be easily obtained by operating the gain adjuster.

Also, when both IM and NF are relatively severe,
Since the optimal point is approximately halfway between the limit points of IM and NF, the adjustment is much simpler than blind adjustment, and is useful for basic judgment of the quality of the receiver.

As explained above, the present invention adjusts the high-frequency gain in the attenuation circuit inserted between the stages of the high-frequency amplifier to vary the various sensitivity characteristics of the receiver and the band characteristics of the low-pass filter. Then,
Since these standards can be satisfied by adjusting the amplification gain to any standard required for each purpose, it is possible to shorten the adjustment time during mass production, and the adjustment time can be reduced. It is also simple, does not require the use of a large number of high-level engineers, and can reduce costs by saving labor costs and shortening work time, and has great industrial value.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a radio receiver for mobile communication.
FIG. 2 is a wiring diagram of essential parts of a radio receiver according to an embodiment of the present invention, and FIG. 3 is a characteristic diagram thereof. 2a...first stage amplifier, 2b...second stage amplifier, 4...bandwidth filter.

Claims (1)

[Scope of utility model registration request] The high-frequency amplification section is composed of at least two or more stages of amplifiers connected in tandem, and a series circuit of a coupling capacitor and a resistor is connected between the base of the transistor constituting the rear-stage amplifier of this high-frequency amplification section and the output terminal of the previous-stage amplifier. , the other end of a variable resistor whose one end is grounded via a bypass capacitor and whose movable terminal is connected to the base of the transistor is connected to a connection point between the coupling capacitor and the resistor forming the series circuit; Adjusting the gain of the subsequent stage amplifier by adjusting the variable resistor, changing the sensitivity characteristics and the cross-modulation characteristics in conjunction with each other in opposite directions,
A radio receiver configured to conform to a predetermined standard, and configured to configure a low-pass filter by the function of the bypass capacitor to prevent a subsequent stage amplifier from causing unnecessary oscillation.