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参数资料
| 型号： | SA1630 |
| 厂商： | NXP Semiconductors N.V. |
| 英文描述： | IF Quadrature Transceiver(IF正交收发器) |
| 中文描述： | 中频正交收发器（中频正交收发器） |
| 文件页数： | 18/36页 |
| 文件大小： | 477K |
| 代理商： | SA1630 |
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Philips Semiconductors
Application note
AN2003
SA1630 IF transceiver demonstration board
1999 Jan 05
18
Receive path
Q: How do I determine the Rx voltage gain
A: The receive voltage gain is defined as G
v
= 20 log (V
outrms
/V
inrms
).
Program the IC for maximum Rx gain and increase the input
power to the RF
in
port until a 1V
p-p
output is obtained. V
outrms
in
the above equation is then equal to (1V
p-p
/2)*0.707. Next, V
inrms
needs to be determined. The rms voltage at the RF
in
port and
the primary of the balun transformer is equal to
V
portrms
= [10^(Pin/10)*0.05]^1/2 where Pin is given in dBm. The
1:4 impedance balun transformer will double this primary input
voltage at the secondary. The next item to be determined is how
much of this rms voltage at the secondary terminals is dropped
across the Rx differential input pins. The differential input
impedance between these pins is given in the datasheet as
6.6 k
//0.7 pF. This impedance and all impedance’s parallel to it
(i.e., 5.1 k
resistor and 100 nH inductor) represent
approximately 160
impedance at 352 MHz. The voltage at the
secondary of the balun transformer is dropped across this 160
and the impedance of the two 1.8 pF capacitors, which represent
approximately 500
at 352 MHz. So, 160/660 of the voltage at
the secondary is dropped across the Rx input pins. When all of
the above is considered, a rough approximation of V
inrms
is
approximately equal to
1
/
2
of the rms voltage at the port. One
other factor that should also be accounted for is approximately
0.5 dB of insertion loss through the transformer.
Example calculation for a –80 dBm input at 352 MHz to obtain a
1V
p-p
output:
Gv
20log
1Vp-p
2
* 0.707
10
(
80
0.5)
10
* 2 *660
90.8dB
Q: Why is the Rx RF input return loss not optimized
A: The SA1630 has several dB of margin from its max AGC Rx
voltage gain specification. If too large of a signal reaches the RF
Rx input the part will have trouble meeting its distortion
specification. So, the RF input match was detuned to allow the
part to more easily meet both of these specifications.
Q: Why is the Rx mode current higher than the Tx current
A: If the SA1630 is programmed for maximum gain, the Rx mode
current will include a substantial amount of power delivered to
the multiple gain stages.
Q: What are the external AGC program voltages for maximum
and minimum AGC gain
A: AGCmax = C0 – C5 all low
AGCmin = C0 = low, C1–C5 = high.
Q: Why am I not able to obtain the expected AGC gain when
using the external programming pins
A: Incorrect levels placed at pins 7–12 is the most frequent cause
for this problem. The OFF position on the 10 switch DIP package
corresponds to placing a high voltage on the pin.
The OFF
designator on the DIP package should be ignored
because it
often causes the user to program the gain control pins in the
opposite state they intended. The pin voltage levels can be easily
verified at the test point posts provided.
Q: Why is the board not meeting the 3% THD specification
A: The first thing to note is that the 3% distortion specification for
the SA1630 is not “total harmonic distortion”. The ATE testing of
this device measures the fundamental and the first three
harmonics only. When measuring this parameter, care should be
taken to ensure that the Rx output is not being loaded by your
test equipment. This can be done by connecting an active FET
probe between the Rx output connection and the spectrum
analyzer.
Q: Why is my board not meeting the 1.0 V
p-p
output drive
specification
A: As mentioned above, care should be taken not to load the output
with a 50
test equipment port. Also, if you are in the AGCmin
setting, note that the output drive specification for this AGC
setting is specified lower than for the other settings.
Q: What is the impedance transformation of the Rx input
balun
A: The impedance transformation is 4:1.
Q: Why is the frequency response of the Rx path
discontinuous while measuring Rx bandwidth
A: An SMA connector is provided at the Rx output for convenient
connection for monitoring the Rx output signal on a spectrum
analyzer. However, this is not suggested for measuring the
bandwidth of the Rx path because the excessive loading by the
50
test equipment will cause the frequency response to be
erratic. To avoid this excessive loading, this measurement should
be done by connecting an active FET probe between the
spectrum analyzer and the Rx output test point post.
Transmit path
Q: How do I determine the quadrature phase error of the IC
A: First you must calibrate the input tones using a phase gain meter
prior to injecting them into the Tx input ports. Note what the
relative phase between the I and Q signal generators is. Next,
adjust the phase difference between I and Q until the suppressed
sideband reaches its minimum. The difference between the
original phase setting and this new phase setting represents the
quadrature phase error of the IC.
Q: Why am I not obtaining the single sideband suppressed
carrier output I expect
A: In general, degradation in sideband suppression is caused by
either mismatched gain or quadrature phase error between the I
and Q channels. Test modes are available which allow you to
operate each channel independently. This allows you to verify
that both the I and Q channels are operational. Make sure that
you are not in one of these test modes while trying to measure
sideband suppression. Operating just the I or Q channel by itself
yields a double sideband output. Carrier suppression can be
degraded if a DC differential voltage exists at the Tx baseband
inputs. Check to make sure the Tx baseband input DC bias
voltage (approximately V
CC
/2) is properly connected to the
center taps of the balun transformers.
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