JPH04286228A - High-speed rssi monitor circuit - Google Patents

Abstract

PURPOSE:To detect an incoming electric field level at high speed by switching a receiving intermediate frequency filter from a narrow band to a wide band. CONSTITUTION:A circuit to change the second intermediate frequency filter 18 of the narrow band into the wide band at the time of monitoring incoming electric field level RSSI is provided. This circuit is constituted of the second intermediate frequency filter 30 of the wide band installed in accordance with the second intermediate frequency filter 18 of the narrow band, and first and second switches 26, 27 and 31, 32 which are inserted in series to these filters and turn on/off conversely to each other by a switching signal. In this case, the BPF 30 of the wide band is provided besides the band pass filter 18 of the narrow band, and at the time of the RSSI monitor, the band pass filter is switched from the BPF 18 to the BPF 30. At that time, the switches 26, 27 and 31, 32 execute this switching, and if the RSSI monitor switching signal S is H, for instance, the switches 31, 32 are turned on, and the switches 26, 27 are turned off.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high speed RSSI monitor circuit in a digital car telephone. TDMA
Digital car telephones use empty slots during a call to monitor the RSSI level (receiving electric field level) of other channels, report this to the base station, and use it during handoff. The time of an empty slot is only a few mSec, so R
SSI (Receive Signal Strength)
th Indicator) level needs to be detected at high speed.

0002

2. Description of the Related Art A conventional RSSI monitor circuit is shown in FIG. Radio waves from a digital car phone are received by an antenna 11, passed through a bandpass filter (BPF) 12 with a passband of ±25MHz, amplified by a high frequency amplifier 13, and then passed through a BPF 14 with a passband of ±25kHz again.
and then added to the multiplier (first mixer) 15. The other input of the multiplier is the output of the first local synthesizer 20 passed through a ±25 MHz BPF 21. These multiplication results are passed through a ±50KHz BPF (first IF transformer) 16, the output of the BPF is added to a multiplier (second mixer) 17, the product is multiplied by the output of a second local synthesizer (not shown), and the result is ±13KHz BPF
(Second IF transformer) 18 and further passes through an amplifier 19 as a reception output. BPF12, 14, 21 are wideband, dielectric type, BPF16 is wideband, SAW type, B
PF18 is narrow band, ceramic type.

[0003]Using the empty slot during a call, the output frequency of the synthesizer is changed, reception of another channel is performed, and the received output is measured at the output side of the amplifier 19,
Perform RSSI monitoring. The obtained RSSI level is sent to the base station as part of the transmission data and reported. R
The SSI level is used to know which channel has a high RSSI level and to switch to a channel with a high RSSI level during handoff.

0004

[Problem to be solved by the invention] In this conventional method, R
The SSI detection time can only be expected to be about the same time as the synchronization time of the synthesizer 20. Because the reception band is ±13
Since it is a narrow band of KHz, the frequency of the synthesizer is ±
This is because it exhibits a rise characteristic equal to the synchronization time until convergence within 5 KHz. Note that the detection time itself of the RSSI voltage is within 0.5 mS.

[0005] When a conventional narrowband receiver is used as described above, the rise time is comparable to the synchronization time of the synthesizer, and high-speed synchronization of the synthesizer is required to detect the RSSI level at high speed. However, synchronizing the synthesizer at high speed (several mSec) increases the circuit scale and increases costs. Not suitable for miniaturization and low current consumption.

[0006] The present invention improves these points, and allows RSSI to be used without increasing the speed of the local synthesizer.
The purpose is to enable level detection at high speed.

[0007]

[Means for Solving the Problems] As shown in FIG. 1, in the present invention, a BPF (second IF
In addition to transformer) 18, BPF 30, which has a wide band (±50 KHz), is prepared, and BPF 1 is used when monitoring RSSI.
8 to BPF30. switch 26
and 27, 31 and 32 perform this switching, and the RS
If the SI monitor switching signal S is, for example, H, the switch 31,
If the switching signal S is L, the switches 26 and 27 are on, the switches 31 and 32 are off, and the BPF 18 is enabled (normal reception).

[0008]

[Operation] If the receiving BPF has a wide band, the RSSI voltage can be accurately measured even if the synthesizer is in the synchronization process (even if it is not synchronized to an accuracy of within ±1 KHz). The RSSI monitor does not require data reception, so the local synthesizer does not need to be completely frequency synchronized, and the RSSI level can be detected even if it is still in the synchronization (convergence) process. The present invention focuses on this point.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 will be described in detail. In this figure, the same parts as in FIG. 3 are designated by the same reference numerals. Therefore, Figure 1 is the BPF of Figure 3.
Corresponds to 16 and above. As explained in FIG. 3, the BPF is the first IF (intermediate frequency) transformer in the TDMA digital car phone, and the multiplier 17 is the second mixer,
8 is a second IF transformer. In FIG. 1, buffer amplifiers 25, 28, 29, and 33 are inserted at the input and output sides of the filter changeover switches 26, 27, 31, and 32, but these are for suppressing load fluctuations when changing the filters.

In the present invention, since the reception intermediate frequency band is widened, the RSSI voltage can be accurately monitored even when the synthesizer is in the synchronization process as shown in FIG. In this figure 2, the synchronization time of the synthesizer is 1 within ±1KHz.
4mSec, 4mSec within ±30KHz,
If you switch the reception filter to a wideband filter such as ±50KHz, the RSS will start as soon as it converges within ±30KHz.
The voltage of I can be measured accurately, so 14mSec → 4m
High-speed monitoring of Sec becomes possible.

[0011]

As explained above, according to the present invention, the incoming electric field level can be quickly changed by switching the reception intermediate frequency filter from narrowband to wideband without using a sophisticated and complicated circuit such as a high-speed synthesizer. RSSI can be detected.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a high speed RSSI monitor circuit of the present invention.

FIG. 2 is a characteristic diagram showing the rise characteristics, etc. of a synthesizer.

FIG. 3 is a block diagram showing a conventional example.

[Explanation of symbols]

Claims (2)

[Claims] 1. A first mixer (15) that mixes a received high frequency signal and the output of a first local synthesizer, a wideband first intermediate frequency filter (16) that passes a first intermediate frequency output from the first mixer, and a second mixer (17) that mixes the output of the filter and the output of the second local synthesizer;
The RSSI monitor circuit includes an intermediate frequency filter (18) and uses an empty slot during a call to change the output of a synthesizer and monitor the RSSI level of another channel on the output side of the second intermediate frequency filter. The high-speed R is characterized by being equipped with a circuit that changes the band-wide second intermediate frequency filter to a wide-band band during RSSI monitoring.
SSI monitor circuit. [Claim 2] A circuit for changing a narrow band second intermediate frequency filter to a wide band narrow band second intermediate frequency filter (
18), and first and second switches (26 and 27. The high-speed RSSI monitor circuit according to claim 1, comprising: 27, 31, and 32).