la1175 Sanyo Semiconductor Corporation, la1175 Datasheet - Page 14

• Manufacturer Part Number: la1175
• Description: Fm Mixer, If, Agc Driver, Buffer For Car Radios, Stereo Systems
• Manufacturer: Sanyo Semiconductor Corporation

Relation between keyed AGC and two AGC loops
Application circuit used in a very strong field
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
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.
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 (V
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.
2. The LA1175, 1175M are operated from dual supplies (Most ideal).
3. The application circuit shown below is used.
(Must be balanced with the detection band of the wide-band AGC)
This catalog provides information as of September, 1997. Specifications and information herein are
subject to change without notice.
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.
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.
Information (including circuit diagrams and circuit parameters) herein is for example only; it is not guarant-
No products described or contained herein are intended for use in surgical implants, life-support systems,
Anyone purchasing any products described or contained herein for an above-mentioned use shall:
Undesired signals 1, 2
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.
Weak field
Strong field (Field strength in which the ANT circuit may cause
intermodulation to occur)
Make the resistor
value as small as
possible.
LA1175, 1175M
CC
MIX=12V, other=8V) heretofore in use. IF an
(add)
Unit (capacitance : F)
No.2276-14/14