LA1175 Просмотр технического описания (PDF) - SANYO -> Panasonic

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LA1175

FM front end for car radio, home stereo application

SANYO -> Panasonic 

LA1175, 1175M

Relation between keyed AGC and two AGC loops

For the LA1170, keyed AGC provides AGC attenuation control (RF MOS FET 2nd gate). For the LA1175, 1175M,

however, there are two AGC loops as shown above. Therefore, keyed AGC must be applied to both of the two AGC

loops. The LA1175, 1175M contain the ANT damping circuit to improve intermodulation in a strong field, but the

prevention of intermodulation in a strong field and the improvement of the sensitivity suppression characteristic by

keyed AGC are mutually exclusive as mentioned below.

Conditions Desired signal

Weak field

Undesired signals 1, 2 Strong field (Field strength in which the ANT circuit may cause

intermodulation to occur)

If keyed AGC is operated to cause AGC-OFF mode to be entered when a desired signal is received, the varactor in the

ANT circuit may be distorted and intermodulation may occur, which means that it is meaningless for the LA1175,

1175M to contain the ANT damping circuit because it produces no effect. Therefore, the effect of the keyed AGC

circuit in the LA1175, 1175M on the ANT damping circuit is made less than that in the LA1170 so that the above-

mentioned problem does not arise. However, if the LA1175, 1175M are used under the same conditions as for the

LA1170 (no ANT damping, pin 6 open), keyed AGC is operated in the same manner as for the LA1170.

Application circuit used in a very strong field

Since the LA1175, 1175M are designed to be operated from single supply, the dynamic range of the MIX output

becomes narrower as compared with the dual-supply type (VCC MIX=12V, other=8V) heretofore in use. IF an

adjacent interference channel signal is very strong, the intermodulation characteristic at ∆f=400kHz is deteriorated,

because the dynamic range of the MIX output exceeds the limit, which causes a distortion to occur.

The following three countermeasures are available.

1. Q of the MIX coil is made higher to provide a higher selectivity.

(Must be balanced with the detection band of the wide-band AGC)

2. The LA1175, 1175M are operated from dual supplies (Most ideal).

3. The application circuit shown below is used.

Make the resistor

value as small as

possible.

(add)

Unit (capacitance : F)

No products described or contained herein are intended for use in surgical implants, life-support systems,

aerospace equipment, nuclear power control systems, vehicles, disaster/crime-prevention equipment and

the like, the failure of which may directly or indirectly cause injury, death or property lose.

Anyone purchasing any products described or contained herein for an above-mentioned use shall:

Accept full responsibility and indemnify and defend SANYO ELECTRIC CO., LTD., its affiliates,

subsidiaries and distributors and all their officers and employees, jointly and severally, against any

and all claims and litigation and all damages, cost and expenses associated with such use:

Not impose any responsibilty for any fault or negligence which may be cited in any such claim or

litigation on SANYO ELECTRIC CO., LTD., its affiliates, subsidiaries and distributors or any of

their officers and employees jointly or severally.

Information (including circuit diagrams and circuit parameters) herein is for example only; it is not guarant-

eed for volume production. SANYO believes information herein is accurate and reliable, but no guarantees

are made or implied regarding its use or any infringements of intellectual property rights or other rights of

third parties.

This catalog provides information as of September, 1997. Specifications and information herein are

subject to change without notice.

No.2276-14/14

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