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參數(shù)資料
| 型號： | MC13030 |
| 廠商： | Motorola, Inc. |
| 英文描述： | DUAL CONVERSION AM RECEIVER |
| 中文描述： | 二次變頻接收機(jī)上午 |
| 文件頁數(shù)： | 9/16頁 |
| 文件大?。?/td> | 386K |
| 代理商： | MC13030 |
MC13030
9
MOTOROLA ANALOG IC DEVICE DATA
PIN FUNCTION DESCRIPTION (continued)
Pin No.
Description
Internal Equivalent Circuit
26
VCC
Vref
26
75
VCO Reference
The first oscillator coil is connected from Pin 26 to 27. Pin 26 must be
bypassed to ground with a capacitor which has a low impedance at the
oscillator frequency. This capacitor also will reduce the phase noise of
the VCO.
27
7.5 k
27
to Mixer1
VCO
The VCO is a negative resistance type and has an internal level control
circuit so a tapped coil or one with a secondary is not needed. The level
is fixed at 0.8 Vpp so the oscillator signal does not modulate the tuning
diode, thus keeping the distortion low. The oscillator stray capacitance is
≈
12 pF and the tuned circuit impedance should be greater than 3.0 k to
guarantee oscillation. Oscillator range is up to 45 MHz so it can be used
for SW receivers.
28
100
28
VCO Out
The output level is 240 mVrms (108 dB
μ
), high enough to drive any
CMOS synthesizer.
AM CAR RADIO DESIGN NOTES
The MC13030 AM Radio IC is intended for dual
conversion AM radios. In most cases, the 1st IF frequency
(FIF1) is upconverted above the highest input frequency. The
first oscillator (VCO) is tuned by a synthesizer and operates
at Fin + FIF1. For the 530 to 1700 kHz AM band with a
10.7 MHz first IF, the VCO goes from 11.23 to 12.40 MHz.
Therefore, Fmax/Fmin for VCO is only 1.104, so one low–cost
tuning diode can be used. Since the required tuning voltage
range can be made less than 5.0 V, it may also be possible to
drive the tuning diode directly or from the phase detector of
the synthesizer IC, such as the Motorola MC145170,
operating from 5.0 V, without using a buffer amplifier or
transistor.
If the VCO is above the incoming frequency, the image
frequency of the first mixer is at fOSC + FIF1. For the AM
broadcast receiver, it is around 22 MHz, so a simple LPF
can be used between the RF stage and Mixer1 input.
However, if a LPF is used, an additional coil is still needed
to supply the collector voltage of the RF amplifier. For this
reason, a BPF filter was used in the application circuit
instead, since it uses the same number of coils and gives
better performance. It is simply a lowpass to bandpass
conversion. The lowpass filter is designed to have a cutoff
frequency equal to the desired bandwidth. In this case, it
would be 1700 – 530 kHz = 1170 kHz. Then, it is
transformed to be resonant at 949 kHz, the geometric
mean of the end frequencies:
A balanced–to–unbalanced transformer is required at the
output of both mixers. The first one is designed so that Mixer1
has enough gain to overcome the loss of the 10.7 MHz filter
and so that the output of the mixer will not overload before the
input. The primary impedance of the transformer is relatively
low, and it may be difficult to control with commonly available
7.0 mm transformers because the number of primary turns is
1700 x 530 = 949 kHz.
quite small. It would also require a large tuning capacitance.
A better solution is to tune the secondary with a small
capacitance and then use a capacitive divider to match the
tuned circuit to the filter. This allows one transformer to be
used for either a ceramic or crystal filter. The capacitors can
be adjusted to match the filter. The recommended coil is
made this way.
If the formula: Pin = IP3 – DR/2 is used, the maximum input
level to the mixer can be calculated for a desired dynamic
range.
IP3 = 3rd order intercept level in dB (dBm or dB
μ
)
DR = dynamic range in dB between the desired signals
and 3rd order intermodulation products
Pin = input level in dBm or dB
μ
The RF AGC level can then be adjusted so that Pin does
not exceed this level.
Whether or not a narrow bandwidth crystal or wide
bandwidth ceramic filter is used between the first and second
mixers depends on the receiver requirements. It is possible to
achieve about 50 dB adjacent channel and IM rejection with
a ceramic filter because of the wide dynamic range of the
mixers. If more than this is required, a crystal filter should be
used. If a crystal filter is used, a lower cost CFU type of
455 kHz second IF filter can be used. If a ceramic filter is
used, a CFW type filter should be used because there is no
RF section selectivity in this type of radio.
Since the wideband AGC system is quite sensitive, it can
be set to eliminate all spurious responses present at the
receiver output. However, the RF AGC will sometimes
eliminate or reduce the level of desired signals if there is a
strong signal somewhere in the bandpass of the RF circuit.
The second mixer is designed like the first and requires a
balanced output. Since its load impedance is higher, the
transformer can be designed to be tuned on the primary or
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