LA1245.PDF

Ordering number : EN737F

Monolithic Linear IC

LA1245

AM Electronic Tuner

Overview

LA1245 is a high performance IC to be used as an AM

electronic tuner. It provides an automatic search-stop

signal, local oscillator buffer-output, and the low level

local oscillation, as well as providing all other functions

required of an AM tuner. Moreover, the stable local

oscillation from LW to SW facilitates the use of many

band.

Functions

• RF amplifier • MIX • OSC (with ALC) • Detection

• IF amplifier • AGC • Local oscillation buffer-output

• Signal meter driving output (also used as an automatic

search stop-signal)

• etc.

Package Dimensions

unit : mm

3021B-DIP20S

[LA1245]

SANYO: DIP20S

Features

• Narrow-band signal meter : Available as an automatic search-stop signal (also available as a wide-band signal

meter). Signal meter output=1/2 frequency ±1.5kHz typ.

• Local oscillation buffer-output : Facilitates the design of electronic tuning systems and frequency representation.

• OSC (with ALC) : The oscillation output is stabilized at a low level (350 mVrms) for a varactor

diode, and tracking error is minimized.

• RF amplifier : Excellent in usable sensitivity by incorporating low-noise transistors in cascode

circuit (45dB/m typ).

• MIX : Double balanced differential MIX prevents the influence of spurious radiation and

IF interferences (IF interference = 85dB typ).

• Low noise : Excellent in S/N for intermediate input (57dB typ).

• Compensation for V CC fluctuation : Allows little gain fluctuation and little distoriton fluctuation (8 to 16 V).

• Low shock noise

: Able to decrease the shock noise by selecting AGC time constant when changing

V CC -on and/or switching the mode.

SANYO Electric Co.,Ltd. Semiconductor Bussiness Headquarters

TOKYO OFFICE Tokyo Bldg., 1-10, 1 Chome, Ueno, Taito-ku, TOKYO, 110 JAPAN

63097HA (KOTO)/33194HO/N050JK/8044KI,TS3173KI/O020KI No.737-1/11

LA1245

Specifications

Maximum Ratings at Ta=25°C

Parameter

Symbol

Conditions

Ratings

Unit

Supply voltage

V CC max

Pin 8, 14

Output voltage

V o

Pin 5, 7

Input voltage

V I

Pin 3

5.6

Supply current

I CC max

Pin 5+7+8+14

Output high drive current

I 18

Pin 18

I 20

Pin 20

Allowable power dissipation

Pd max

See Figure 2

700

Operating temperature

Topr

–20 to +70

°C

Storage temperature

Tstg

–40 to +125

°C

Recommended Operating Conditions at Ta=25°C

Parameter

Symbol

Conditions

Ratings

Unit

Recommended supply voltage

V CC

Operating Characteristics at Ta=25°C, V CC =12V, f r =1MHz, f m =400Hz, at specified test circuit

(based on application circuit).

Parameter

Symbol

Conditions

Ratings

Unit

min

typ

max

Current drain

I CC 1

quiescent

16.0

25.0

35.0

I CC 2

107 dBµ input

19.0

29.0

40.0

Detection output

V o 1

23 dBµ input, mod. 30%

–27.5 –23.0 –18.5 dBm

V o 2

80 dBµ input, mod. 30%

–15.5 –12.5

–9.5 dBm

Signal to noise ratio

S/N1

23 dBµ input, mod. 30%

S/N2

80 dBµ input, mod. 30%

Total harmonic distortion

THD1

80 dBµ input, mod. 30%

0.4

1.0

THD2

107 dBµ input, mod. 30%

0.3

1.0

Signal meter output

V SM 1

quiescent

0.5

V SM 3

107 dBµ input

3.0

4.5

7.0

Input at signal meter output=1V V IN 1

V SM output=1V

19.0

25.0

31.0 dBµ

Local oscillation-buffer output

V osc

250

350

mVrms

Reference Characteristics

Parameter

Symbol

Conditions

Ratings

Unit

min

typ

max

Signal meter output

V SM 2

40 dBµ input

2.5

Total harmonic distortion

THD3

112 dBµ input, mod.30%

Local oscillation fluctuation

Æ V osc

V osc L (522kHz) to V osc H

mVrms

within a band

(1647kHz)

Signal meter band width*

V SM-BW1

80 dBµ input, 1/2 output frequency

±1.5

kHz

V SM-BW2

80 dBµ input, 1/10 output frequency

–4.5/+7

kHz

Selectivity

±10kHz at 30% mod.

IF interference

f r =600kHz

Image frequency interference

f r =1400kHz

ratio

* BFB450C4 N (Murata, Co.,) was used as a narrow band filter.

(Note) 0 dBm=775mV, 0 dBu=1µV.

No.737-2/11

LA1245

Using the automatic search-stop signal

Signal Meter-driving output circuit is equivalent to Figure. 1, signal meter driving output (abbreviated as V SM ) is

narrowed in band width and can be used as an automatic search-stop signal when a narrow band series resonator is

connected to pin 15. V SM can be adjusted with R 208 and R 211 both in wide band and narrow band since R 208 is

inversely proportional to V SM , while R 211 is proportional to V SM . R 208 is related to the Q of narrow band signal

meter. When the resistance of R 208 is increased, the Q will be damped and the band width increased. On the other

hand, R 211 used as the output impeadance of V SM and affects the cut-off frequency and time constant of low pass

filter for V SM and the meter drive impedance. The time constant

and the cut-off frequency fc can be expressed as

follows :

= (C 114 +C 115 +C S ) (R 211 //R in )

f c = 2

¹t

A semi-fixed resistor is recommended to be used as R 211 to cope with the fluctuation of V SM . Refer to Figure. 3 for

the value of the semi-fixed resistor since this depends upon V SM and R 208 . Figure. 3 shows the lowest limit of the

semi-fixed resistor in relation to R 208 with the parameter of V SM set point, and the value of the semi-fixed resistor

will be equal to or greater than that shown in Figure. 3. For example, when V SM =5V and R 208 =240

, R 211 becomes

. When the value of V SM is too large,

it is limited and saturated to the source voltage so it is recommended to follow the condition of V SM ²

. Thus, the value of the semi-fixed resistor is determined to be about 30k

V CC –2(V).

When a narrow band serial resonator is used, include the resonant impedance to determine the value of R 208 .

No.737-3/11

28k

LA1245

Notes on LA1245 usage

1. When suddenly tuned to a broadcasting station of intermediate or high field strength, a large current of high frequency

flows into the signal meter circuit, causing the local oscillator malfunctions and abnormal noises.

To eliminate this :

· Use R 208 ³

240

for manual tuning type.

, and use the local oscillation coil at the 1/3 tap (except SW) for electronic tuning type (which uses a

narrow band filter).

2. Use the bias on the condition RF V CC ²

IF V CC , since abnormal noise levels might be caused when detuning a strong

V CC –2 (V) to avoid saturation caused by V CC .

4. Use 1/2 or more tap of LW and MW oscillation coil to improve S/N and the detuning characteristics of the distortion

ratio.

5. Use the full-tap of SW oscillation coil, to allow the sag in oscillation power by the decreasing of Q.

6. Avoid the coupling of the antenna tuning circuit and the local oscillating circuit so as not to leak the local oscillation

into the antenna tuning circuit.

7. Connect the detection capacitor C 113 between pin 13 (output) and pin 14 (V CC ) to avoid the leakage of the IF signal

into the GND line. Connection between pin 13 and pin 12 (GND) increases the tweet interference and deteriorates the

usable sensitivity.

Moreover, depending on the positions of C 113 and the bar antenna, higher harmonics having twice or three times the

frequency of the IF signal may pass into the antenna and cause tweet interference, and in extreme cases oscillation

might be cause. To prevent this :

· Shorter lead wires and connect them near 13 and 14 pins.

· Place C 113 far from the antenna.

No.737-4/11

· Use R 208 ³

input on the codition RF V CC >IF V CC .

3. Use the signal meter driving output (V SM ) at V SM ²

LA1245

9. Use a semi-fixed resistor for R 211 to allow the fluctuation of V SM .

10. When changing an IFT or using an RF tuner, select a filter and related circuits according to the following conditions.

The input levels of each terminal where 30% modulated detection output of –25dBm is obtained are as follows :

Pin 11 input

when Rg=520

(470

+ 50

)

75dBµ

Pin 9 input

when Rg=50

53dBµ

Pin 6 input

when Rg=50

48dBµ

22dBµ

Slight change in IFT, however, will be covered by changing the constant of resistors R 202 and R 204 .

11. When the coupling coefficient of the local oscillation coil is small and an anti-resonance point of about 100MHz is

present or the stray capacitance between pin 19 and pin 20 is large, the buffer output (pin 20) may be subject to

parasitic oscillation of about 100MHz. In this case, connect a capacitor of about 30pF between pin 20 and GND. To

observe parasitic oscillation, connect a capacitor of 5pF in series with the probe. If the probe is connected direct to

pin 20, the input capacitance of the probe causes parasitic oscillation to stop, which makes it impossible to observe.

when Rg=50

Sample Application Circuit 1

Unit (resistance :

, capacitance : F)

No.737-5/11

8. When a cable or something similar is connected to a local oscillation buffer (pin 20), which is equivalent to

connecting a capacitor of about 20pF, the output from the buffer will be of sawtooth waves, causing the level low at

the short wave band. To prevent this, connect a resistor between pin 20 and GND, which will increase the operating

current of the buffer amplifier. Since the maximum current obtained from pin 20 is 2mA, the suitable resistance

between pin 20 and GND is 1.5k

Pin 3 input

Plik z chomika:

Inne pliki z tego folderu:

Inne foldery tego chomika: