 Low IF Architecture Adopted |
|
In conventional can tuners, 58 MHz is used as
the IF (intermediate frequency) and a SAW
filter (surface acoustic wave) is used as the
channel filter. Since the pass band
characteristics are determined by the physical
parameters, the SAW filter has the
disadvantage that it cannot be made smaller
than a certain fixed size.
By selecting 4 MHz as the IF, the
CXA3746ER is able to integrate a filter with
the same sharp selectivity characteristics as
SAW filters on the same chip and thus obviate
the need for the SAW filter.
Furthermore, a newly-developed circuit is
adopted as the output circuit to achieve low
distortion and a high output dynamic range. |
| High Sensitivity and Excellent
Interference Rejection |
|
The CXA3746ER integrates an RF tracking
filter and can implement a high-Q RF filter
for extremely high rejection of interfering signals. Sony repeatedly performed simulations
for RF filter impedance matching and to reduce
the input resistance and achieved a low noise
figure (NF = 4 to 6 dB) by optimizing the
FET device. This allowed the CXA3746ER
to achieve a high sensitivity. |
RF Level Detection Circuit and
RF AGC
|
|
Another method for achieving excellent
interference rejection is to detect the level of
the broadcast signal waveform input from the
antenna and to automatically lower the gain
when that signal has a high level, thus
adjusting the mixer input to have an optimal
value so that distortion does not occur. The
CXA3746ER adopts this self-AGC
mechanism. |
| Low Phase Noise Built-in VCO
and PLL |
|
While a resonator circuit consisting of on-chip
inductor and varactor devices is built in, the
CXA3746ER features a VCO with superlative
phase noise performance.
The CXA3746ER achieves at the same time
both the phase noise away from the carrier
(100 kHz and over offsets) required for analog
broadcast reception and the phase noise in the
vicinity of the carrier (under 10 kHz offsets)
required for terrestrial digital broadcast
reception by adopting a dual-mode PLL that
provides both fractional-N PLL and integer
PLL modes. |
| Low Spurious Signals |
|
Spurious signals*1 are a major problem for
tuners that handle high-frequency wide
bandwidth signals from 90 to 770 MHz.
Especially for analog broadcast reception,
when the spurious signals are in the reception
signal band, they can appear as noise in the
image.
Sony designed the circuit structures and chip
layout in the CXA3746ER to suppress spurious
signals so that it could also be used with analog
broadcasts. As a result it achieves an input
converted spurious signal level of -130 dBm or
lower.
*1: Spurious signal: Frequency components due to
interference between signal, high-frequency
leakage from local oscillators, and other factors
that can have an adverse influence on reception. |
Silicon Tuner IC for Analog and Terrestrial
Digital TV Broadcast Features Superlative
Sensitivity and Interference Rejection
Vol.52