MC13155D 查看數據表（PDF） - Motorola => Freescale

零件编号

产品描述 (功能)

生产厂家

MC13155D

Wideband FM IF

Motorola => Freescale 

Freescale SMeCm1i3c15o5nductor, Inc.

Quadrature Detector

The quadrature detector is coupled to the IF with internal

2.0 pF capacitors between Pins 7 and 8 and Pins 9 and 10.

For wideband data applications, such as FM video and

satellite receivers, the drive to the detector can be increased

with additional external capacitors between these pins, thus,

the recovered video signal level output is increased for a

given bandwidth (see Figure 11A and Figure 11B).

The wideband performance of the detector is controlled by

the loaded Q of the LC tank circuit. The following equation

defines the components which set the detector circuit’s

bandwidth:

Q = RT/XL

(1)

where: RT is the equivalent shunt resistance across the LC

Tank and XL is the reactance of the quadrature inductor at the

IF frequency (XL = 2πfL).

The inductor and capacitor are chosen to form a resonant

LC Tank with the PCB and parasitic device capacitance at the

desired IF center frequency as predicted by:

fc = (2π √(LCp)) –1

(2)

where: L is the parallel tank inductor and Cp is the equivalent

parallel capacitance of the parallel resonant tank circuit.

The following is a design example for a wideband detector

at 70 MHz and a loaded Q of 5. The loaded Q of the

quadrature detector is chosen somewhat less than the Q of

the IF bandpass. For an IF frequency of 70 MHz and an

IF bandpass of 10.9 MHz, the IF bandpass Q is

approximately 6.4.

Example:

Let the external Cext = 20 pF. (The minimum value here

should be greater than 15 pF making it greater than the

internal device and PCB parasitic capacitance, Cint ≈

3.0 pF).

Cp = Cint + Cext = 23 pF

Rewrite Equation 2 and solve for L:

L = (0.159)2 /(Cp fc2)

L = 198 nH, thus, a standard value is chosen.

L = 0.22 µH (tunable shielded inductor).

The value of the total damping resistor to obtain the

required loaded Q of 5 can be calculated by rearranging

Equation 1:

RT = Q(2πfL)

RT = 5 (2π)(70)(0.22) = 483.8 Ω.

The internal resistance, Rint between the quadrature tank

Pins 8 and 9 is approximately 3200 Ω and is considered in

determining the external resistance, Rext which is calculated

from:

Rext = ((RT)(Rint))/ (Rint – RT)

Rext = 570, thus, choose the standard value.

Rext = 560 Ω.

SAW Filter

In wideband video data applications, the IF occupied

bandwidth may be several MHz wide. A good rule of thumb is

to choose the IF frequency about 10 or more times greater

than the IF occupied bandwidth. The IF bandpass filter is a

SAW filter in video data applications where a very selective

response is needed (i.e., very sharp bandpass response).

The evaluation PCB is laid out to accommodate two SAW

filter package types: 1) A five–leaded plastic SIP package.

Recommended part numbers are Siemens X6950M which

operates at 70 MHz; 10.4 MHz 3 dB passband, X6951M

(X252.8) which operates at 70 MHz; 9.2 MHz 3 dB passband;

and X6958M which operates at 70 MHz, 6.3 MHz 3 dB

passband, and 2) A four–leaded TO–39 metal can package.

Typical insertion loss in a wide bandpass SAW filter is 25 dB.

The above SAW filters require source and load

impedances of 50 Ω to assure stable operation. On the PC

board layout, space is provided to add a matching network,

such as a 1:4 surface mount transformer between the SAW

filter output and the input to the MC13155. A 1:4 transformer,

made by Coilcraft and Mini Circuits, provides a suitable

interface (see Figures 16, 17 and 18). In the circuit and

layout, the SAW filter and the MC13155 are differentially

configured with interconnect traces which are equal in length

and symmetrical. This balanced feed enhances RF stability,

phase linearity, and noise performance.

MOTOROLA ANALOG IC DEVICEFDoArTMA ore Information On This Product,

11

Go to: www.freescale.com

Share Link: