JPS604334A - Radio receiver of frequency conversion type - Google Patents

Abstract

PURPOSE:To improve the saturation characteristic without having a bad influence upon an overall noise factor by reducing the gain of a radio frequency amplifier and increasing the gain of an intermediate frequency amplifier at the time when the saturation of the output level of the intermediate frequency amplifier is started. CONSTITUTION:When an RF input level is increased, the output level of an intermediate frequency amplifier IFA4 is increased linearly; and when this output level exceeds a certain level, a frequency converter MIX and succeeding stages of the IFA4 start being saturated to generate a transmission distortion. A level detector 5 detects this saturation start level and drives a switch 1S to turn on an attenuator 1A and drives a switch 4S to turn off an attenuator 4A. In this case, if values of the attenuation quantity of the turned-on attenuator 1A and the attenuation quantity of the turned-off attenuator 4A are set to the same value, they are cancelled mutually, and the output level of the IFA4 is not changed. Consequently, the saturation of the MIX and the IFA is avoided, and a bad influence upon the whole of a receiver is prevented.

Description

Detailed Description of the Invention (a) Technical Field of the Invention The present invention relates to a radio receiver in which the input level of a radio frequency signal can vary widely, and in particular, to a radio receiver of a frequency conversion type that has a low overall noise figure. This relates to the circuit configuration of the receiver.

(b) Prior Art and Problems A conventional frequency conversion wireless receiver has a circuit configuration as shown in FIG.

The radio frequency signal input Rpin is first connected to a radio frequency amplifier (RF
A) After being amplified by 1, it is mixed with the output of local oscillator (LO) 3 and frequency converter (MIX) 2 to produce an intermediate frequency signal (
It is converted into an IF multiplied signal lif. This IF multiplied signal if
is amplified by an intermediate frequency amplifier (IFA) 4 to a level necessary to drive the next stage demodulator or another frequency converter (none of which is shown). The output signal ``li'out'' of the intermediate frequency amplifier (IFA) 4 will not be distorted unless it is a signal with little noise and little distortion.

Noise figure (abbreviated as NF) that represents the noise characteristics of the frequency conversion type wireless receiver having the above configuration.
In order to lower the NF, a first stage RFA with a small NF is generally used.

RFA with large amplification gain, MIX with low conversion loss.

This can be seen in the first stage circuit of an IFA with a small NF and the first stage IFA with a large amplification gain. Among these, MIX with low conversion loss,
Since the first stage amplifier of IFA with small NF has a limit due to economic efficiency, as a way to improve these values isometrically, RFA with large amplification gain and first stage IFA with large amplification are adopted to reduce noise. It's here. However, if the amplification of these RFAs or first-stage IFAs is increased, the RF
When the input level becomes high, level saturation occurs at the subsequent stage of MIX and IF'A, resulting in amplitude distortion and phase distortion. To avoid this, the circuit must be constructed using high-output RF'A or IFA with a high saturation level, but this has drawbacks such as increased power consumption and expensive components. ing.

(C) Object of the Invention The object of the present invention is to eliminate the above-mentioned drawbacks and to provide an economical radio receiver with a low integrated noise figure and good saturation characteristics even with large fluctuations in the receiving input level. be.

(d) Structure of the Invention In the present invention, first, the input level of the radio frequency signal to the receiver (
When the RF large input is low, the amplification gain of the radio frequency amplifier (RFA) is kept large in order to improve the noise figure (NF), and then when the RF large input becomes high, the intermediate frequency amplifier (IFA) is
) starts to saturate, the amplification gain of the RFA is lowered at that point, and the amplification gain of the IFA system is lowered instead, leaving the overall amplification gain unchanged, as follows. Configure the circuit. That is, a first RF attenuator that attenuates the radio frequency level and an RF switch that controls attachment/detachment (on/off) of the first RF attenuator are provided at the output stage of the radio frequency amplifier (RFA). Next, the output stage of the pre-intermediate frequency amplifier is also provided with a second IF attenuator that attenuates the IP' (II level) and an IF switch that turns it on and off. A level detector for driving is provided at the output stage of the front IW intermediate frequency amplifier 11, detects the point at which the linear amplification of the IW signal output is lost and saturation starts, and activates the first RF attenuator. On, second IF
Configure the circuit to turn off the attenuator.

(e) Embodiments of the Invention Below, Fig. 2 shows an example of a circuit for frequency conversion type radio reception based on the present invention, and saturation characteristics of received signal input level (RF'in) and intermediate frequency amplifier output level (IFout). This will be explained with reference to FIG.

In FIG. 2, IA is the first attenuator, IS is the first switch, 4A is the second attenuator, and 4S is the second switch.

1 and 5 are level detectors, which are circuits that are replaced with conventional circuits in the present invention. For numbers other than the above,
The same circuits as the numbers in the conventional circuit of FIG. 1 are shown.

When the level of the receiver's radio frequency signal input (RF input) is low, the first attenuator IA of the output circuit of the radio frequency amplifier (RFA) is turned off, and the output circuit of the intermediate frequency amplifier (IFA) is turned off. The second four attenuators are set to the on state by the level detector 5.

When the RF input level increases, the output level T of IFA4 increases.
F ont increases linearly as shown in Fig. 3(a), but from the level Ps of the RF input level in Fig. The curve becomes as shown in b), and various transmission distortions begin to occur in the F person's output signal. At this time, the level detector 5 detects this saturation start level Ps at the output stage of the IFA 4 (or a level in the linear portion may be selected considering an appropriate operating margin), and drives the switch IS. to turn on the attenuator IA and drive the switch 4S to turn on the attenuator 4A.
is off. If the attenuators of one attenuator that is turned on and the attenuator 4A that is turned off have the same attenuation value, they will cancel each other out and the output level of IFA4 will be attenuated %iT as shown in Figure 3(c). Just shift it horizontally to the left by that amount and it won't change.

Therefore, saturation in WI I
It extends as shown in FIG. 3(d). As for the RF input level, the permissible variation range is expanded by a significant level for the value of the attenuator T.

On the other hand, in the case of noise sum, the RF signal power level is already high at the time P8 when switches Is and 4S are activated, and the signal-to-noise ratio is close to a large value, so the attenuator IA is
Even if it is inserted into the output of A, there is no adverse effect on the receiver integration.

Needless to say, the above configuration can be commonly used for modulation formats such as AM, F'M, and PSK.

(f) Effects of the Invention As detailed in the embodiments, according to the present invention, a power line receiver with low saturation and good noise characteristics can be used for any modulation format even when the fluctuation range of the received input level is large. The effect is great because it can provide support even if

[Brief explanation of the drawing]

FIG. 1 is a conventional circuit, FIG. 2 is a circuit diagram of a frequency converting radio receiver according to the present invention, and FIG. 3 is a diagram of input level versus output level. In the figure, 1 is a radio frequency amplifier, 2 is a frequency converter,
3 is a local oscillator, and 4 is an intermediate frequency amplifier. 5 is a level detector, IA, 4A is an attenuator, IS. 4S is a switch. Mine 1 Kuko 2 Monkan 3 Ku Ps X'F; tag

Claims (1)

[Claims] One radio frequency amplifier, one local oscillator, and one frequency converter. In a frequency converting radio reception device consisting of an intermediate frequency amplifier, a first attenuator that attenuates the radio frequency signal level at the output stage of the radio frequency amplifier, a switch that controls the attachment/detachment of the first attenuator, and an intermediate frequency at the intermediate stage of the intermediate frequency amplifier. A second attenuator that attenuates the signal level, a switch that controls attachment and detachment of the attenuator, and a level detection circuit that monitors the intermediate frequency signal level, detects the saturation point of the level, and drives the first switch and the second switch. A frequency conversion type wireless receiving device characterized by comprising: