JPS6331312A - Duplicate pll circuit - Google Patents

Abstract

PURPOSE:To obtain a miniaturized duplicate PLL circuit having superior profitability, by providing a second PLL circuit which performs the control of a temperature controlled crystal oscillator(TCXO) by detecting the deviation of an itermediate frequency. CONSTITUTION:On a crystal oscillator 22 of n-times an IF frequency, a fixed frequency divider 23 of 1/n times the IF frequency, a phase comparator 21, an LPF2 24, and the TCXO, an adjusting voltage Vf which supplies frequency deviation, for example, within 3X 10<-6>, and a switch SW which switches the output of the phase comparator 21, and the Vf, are provided. When a reception input is below the setting level of a squelch control part 10, a change-over switch 26 is switched so as to impress the adjusting voltage Vf set in advance on the TCXO16. When the reception input (fr) goes to higher than a level set in advance, the squelch control part 10 supplies the output of the phase comparator 21 from the adjusting voltage Vf to the TCXO16 by the change-over switch 26 through the LPF224.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a dual PLL circuit that allows the transmission and reception frequency of a mobile station to asymptotically approach the accuracy of the base station transmission frequency.

Prior Art FIG. 2 shows a radio receiver using a conventional PLL circuit. In FIG. 2, 1 is an antenna, 2 is an RF amplifier, and 3 is a first frequency converter (C1).

4 is the 11th P bandpass filter (BPF' 1 ), 5 is the second frequency converter (C2), and 6 is the second local oscillator (Xo
) 7 is the second IF bandpass filter (BPF'2), 8 is I
f' amplifier, 9 is a frequency detector (DISC), 1o is a squelch control unit (SQC), 11 is a signal amplifier, 12 is a speaker (SP), 16 is a variable frequency control oscillator (VCO)
), 2o is a controller (FC) of the variable frequency divider 17, 17 is a variable frequency divider, 16 is a temperature controlled crystal oscillator (TCXO), 18
is a fixed frequency divider, 14 is a phase comparator (PD), 19 is a low pass filter (LPF) for removing unnecessary frequencies, and 27 is an output to, for example, a PLL circuit for transmission.

Next, the operation of the conventional example will be explained. FIG. 2 is a block diagram of a radio receiver that uses a frequency synthesizer for the first local oscillator. The reception frequency ([r) from antenna 1 is 几F
The signal is amplified by an amplifier 2 and applied to a frequency converter (Ot) 3. fL is added to the first local oscillator from the frequency synthesizer, and fr is converted to the 11th F (fl), which is applied to the second frequency converter (C2) 6 via BPF, 4, and the second local oscillator (fl) is added to the first local oscillator. From the first IP (fl) to the second IF
(f i) and passes through the BPF 27 to the second IF'
After being amplified by an amplifier 8, it is demodulated by a frequency detector 9,
The sound is amplified from a speaker 12 via an amplifier 11. If the level of the reception input (") is low (S/N is degraded), the squelch circuit 10 stops the output to the speaker 12.

The first local oscillation frequency (ft,) is vCO16, variable frequency divider 1
γ, phase comparator (PD) 14, LPF'+19 and TOX
O1e is composed of a PLL circuit consisting of a fixed frequency divider 18 and a frequency controller 20 to the variable frequency divider 17, and the above TOXO 16 maintains the frequency deviation at Δ"=±3×10 when the channel spacing is 26KH2. On the other hand, by keeping the base station transmission frequency at Δt=2X10, the receiving bandwidth Wi is set to 16 KHz.Here, Wl is Wi = 2 (Δp+rm+~Nawatea47
-)=2 (3,5+1+3.6)=16
．． It is given at 2KHz. Now channel spacing is 125KH
In the case where the band is narrowed to z, the reception band Wi needs to be 8KH2, but the frequency deviation in this case needs to be 1×10 or less.

Wi = 2 (ΔF + f m + 2) = 2 (
175+1 +125 )=8KH2 In the above case, if △ is one △r, both become =Q8KH2 and 100100
For O, use an accuracy of 8 x 10 at the operating temperature, e.g. -3
0' to +70'C is required.

Problems to be Solved by the Invention However, in the above conventional PLL circuit, the T
Since the CXO frequency requires tremendous stability of 08 x 10, it has been difficult not only to make it smaller and more economical but also to realize it.

The present invention is intended to solve these conventional problems, and aims to provide a dual PLL circuit that is small, economical, and easy to implement.

Means for Solving the Problems In order to achieve the above object, the present invention provides a dual control system in which the base station frequency is set to about 1x10, which is relatively easy to implement the above standard, and the frequency of the mobile station is pulled in. It is configured to include a PLL circuit.

Operation Therefore, according to the present invention, the T of the PLL circuit of the mobile station
The CXO has the advantage that an oscillator with accuracy and stability of about 3×10 2 is sufficient as in the conventional case.

Embodiment FIG. 1 shows the configuration of an embodiment of the present invention.
22 is a crystal oscillator (XO2) with 0 times the IP frequency, 23
is a fixed frequency divider of 1//rl of the above frequency, 21 is a phase comparator (PD2), 24 is LPF2.26 is the above TOXO
(Vr), for example, the adjustment voltage (Vf) that gives a frequency deviation within 3 × 10, 26 is the phase comparator (PD) 21
A changeover switch (SW) that switches between the output (Vp) and V
, 27 are reference frequency outputs to the transmitting synthesizer. Other symbols similar to those in FIG. 2 represent the same names.

Next, the operation of the above embodiment will be explained. In the above embodiment, when the reception input is below the setting level of the squelch control unit 10, the changeover switch 26 is switched so that a preset adjustment voltage (V'') is applied to the TCXO 16.The reception band in this case The center frequency of "frequency deviation △f from 0.

is shown as below.

ΔfO2 Δfr±ΔrL±△f1・・・・・・・・・(
1) Now, if we add the deviation frequency to this, we get the following.

Δfr: Base station transmission frequency f 7 = 900 MHz
Deviation (1×10)=9Q○H2 △fL: First local frequency rL=(r+90=990MH
Deviation of 2 (3X 1 0) = 2,970 H2
Δft: 1st local oscillation frequency fl: 90 Deviation of MH2 (6×10) = 4501 (z In the above case Δfo = 900+2970 +450 (H2)=
It becomes 3870H2.

The receiving frequency (f, ) is in the range of ±3.87 KHz even in the worst case with respect to the receiving band (±4 KH2), and is barely caught on the shoulder of the receiving band. It is clear that if a modulated wave is input here, large distortion will occur.

When the reception input (fr) reaches a preset level or higher, the squelch control unit 10 uses the changeover switch 26 to supply the output (Vp) of the phase comparator (PD2) 21 from the above-mentioned adjusted voltage (vr) to the TCXO 16 via the LPF 226. do. At this time, if the frequency deviation of the comparison oscillator 22 applied to the first phase comparator 21 is ±1Q×10, then Δfc #5H2 is obtained when the second IP is 455KI (z).

Therefore, the frequency (fc) of the comparison oscillator 22 is as follows.

(Worst value) △fo=△f"+△fl+Δf1+Δfc△
fO length 3,875H2 (average value) Δf'a= Δfr2+ΔrZ2+Δf12
+ΔfC2Δf'o Volume 2,987 H2 Therefore, from the phase comparator (PD2) 21, the deviation voltage (Vp) that corresponds to the deviation of the above Δ'0 and Δf'o is LP.
It is applied to the TCXO 16 via F224 and the changeover switch 2e. The selector switch 28 is a seesaw type analog switch, and changes from Vf to Vp and back according to a control signal from the squelch control section 1Q.

It is switched from Vp to Vf.

PD221, LPF224.5W26, TCXO16,
Fixed frequency divider 18, BPF313, C10, BPF, 4,
When the loop gain including c2s, BPF'27, and second IIi'' amplifier 8 is set to 10, the frequency deviation (Δ'0 - Δ(c)) with respect to the center frequency fo of the reception band is as follows.

(Worst condition) Δf'o= △fr + △fL + △fl +
Δrc) / (1 + k) Cor Δfc Misaki 34 Ryo H2 (Average value) △f'o-[△fr2+ΔfL2+△"12+△fc2
/(1+k), 1-Δfc#266H2 Reception bandwidth B-2 (Δf 10 fm 10 Δfo) worst value
and 6.2KH2 Average value -=6.0KH2 Therefore, the reception bandwidth of the narrowband PM method is 8KHz (±4KH2
There is sufficient margin for I-(Z).

In addition, before the squelch controller operates, in the worst condition, the reception frequency is close to the shoulder of the reception bandwidth, but with the squelch operation, the frequency is pulled within 350Hz with respect to the center frequency (f+o) of the band, resulting in good reception. It will form a state.

Effects of the Invention As explained in the above embodiments, the present invention detects the shift of the intermediate frequency in the receiver and generates a temperature controlled crystal oscillator (TC).
a second PLL circuit that controls the TCXO);
By providing a double PLL circuit of the first PLL circuit controlled by the difference between
As with H2, the stability is good at around 3 x 10, so it has the advantage of hardly increasing the manufacturing cost of mobile devices that require mass production, and is useful for the practical application of narrowband PM systems. There are some very big things.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram of a receiver using a dual PLL circuit according to an embodiment of the present invention, and FIG. 2 is a schematic block diagram of a receiver using a conventional radio receiving PLL circuit. 10... Squelch control section, 14... Phase comparator (P
DP), 1rs=-VCo, 16-TOXO121-I
P PD2.22... Comparison oscillator XO2,26.
- Control voltage source, 26... changeover switch.

Claims (1)

[Claims] installed in the receiver of the mobile station, the output of the VCO is divided by a variable frequency divider and taken out, the output of the temperature controlled crystal oscillator is divided by a fixed frequency and taken out, and compared by a first phase comparator; a first PLL circuit configured to control the output frequency of the VCO by the output of a phase comparator; and a second phase detection circuit that receives the base station transmission frequency and detects a shift in the intermediate frequency of the receiver. and a double PLL circuit including a second PLL circuit configured to control the output frequency of the temperature-controlled crystal oscillator based on the output of the second phase detection circuit.