No. 5736-5/5

LA7775M

Design Notes

1. RF amplifier

This circuit is formed as a two-transistor cascode amplifier and takes an LC tank

circuit as its load. The operating current is set by the external resistor connected to

pin 22. The optimal operating current is between 1.5 and 2 mA. The capacitor

(C2) connected between pins 23 and 24 is related to the tank circuit Q, and must

not be too large.

2. Oscillator circuit

This is a grounded collector oscillator circuit, and supports using either an LC, a crystal, or a SAW resonator. Care is

required when constructing this circuit, since the input sensitivity may be suppressed if the oscillator circuit output

leaks into the IF limiting amplifier. It is extremely important to use a capacitor (e.g. a ceramic capacitor) with

excellent high-frequency characteristics for the 1000 pF bypass capacitor inserted between the oscillator circuit power

supply pin (pin 6) and the ground pin (pin 1). In addition, this capacitor must be located as close as possible to pins 1

and 6. When forming an oscillator circuit using a SAW resonator, the optimal values for C1 through C3 will vary

with the oscillator frequency. Thus this circuit must be adjusted for optimal

performance. Since the capacitor C3 between pin 3 and ground will be shared if a

circuit that switches between two SAW resonators is used, the difference between

the frequencies must be held to under 10 MHz. If a large frequency difference is

required, design a circuit that also switches the capacitance between pin 3 and

ground.

3. IF limiting amplifier

This circuit consists of a six-stage direct coupled differential amplifier to which DC feedback is applied. Since an

internal 1-k

Ω resistor is built in between the IF input pin (pin 9) and pin 11, the input and output impedance of the

330-

Ω IF filter can be matched with an external 510-Ω resistor. No external matching resistor is required for the IF

output (pin 7), since a 330-

Ω resistor is built in.

4. Quadrature detection circuit

An external phase shifting circuit is formed from an LC tuning circuit and a ceramic discriminator.

This catalog provides information as of June, 1997. Specifications and information herein are subject to change

without notice.

s 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 loss.

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

ΠAccept 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 responsibility 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.

s Information (including circuit diagrams and circuit parameters) herein is for example only; it is not guaranteed 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.

21

22

23

C1

C2

T00090

24

3

4

5

C1

C2

C3

T00091

T00092

12

13

12

13

T00093