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OVERVIEW: iDEN Digital Modulation Technology
The Javelin level set circuit topology was modified slightly for Sledgehammer. The modification removed
sw
itches used to select the I-channel training waveform to the Q-channel V-I input. The current level-set
circuitry contains a programmable gain V-I on the I channel for boosting the reference signal level durin
level training. In this configuration, the control signal (cnrmp) is output from the level-set cir
I-
channel V-I to control the point at which the gain is changed.
V_TERM is a new signal input that will be OR'ed with the clip comparator output. This signal causes a
controlled signal to ramp down when the battery current exceeds 3A during level training.
V
_TERM is OR'ed with the clip comparator output and sent back to the digital core to terminate the
counter used for the LEVEL TRAIN read back value. Negative feedback is required to maintain syst
stability. Phase training is done to ensure that the feedback is negative (180
consists of the sum of the delays of several modules and components.
O
peration of the Sledgehammer in a closed loop system requires the phase of the feedback path to be
adjusted with respect to the forward path, such that the demodulated feedback signal is the correct phase at
the summing junction. This adjustment needs to take place before the loop is closed and data is tr
and is referred to as the 'phase training period'.
T
he maximum peak input signal to Sledgehammer is also scaled via the Roadrunner/DSP to insure that the
maximum input signal in the data will not cause clipping to occur in the PA output as a result of
temperature/voltage gain variation in the forward path. The scaling of the input signal is a result of 'level
training' which is performed in the transmit slot prior to data transmission.
The scaling of the input signal and the ramping is performed by the JANUS DSP. The ramp signal will be
applied from the DSP, and then will go through the signal path of the Roadrunn
m
aximum. The loop will be closed, but the slew rate limiter will be in a low gain (low slew) mode. A
counter on the Sledgehammer will begin counting from the beginning of the timing event associated sig
(LAGC) and its associated timing parameter "D". The loop will perform an AGC function in the beginni
portion of the ramp in order to set the loop gain and then hold this gain value.
When the clip detect comparator determines that the loop can no longer compensate for the PA, it will
disconnect the Roadrunner input and allow the slew rate limiter to ramp the signal down in a controlled
manner to prevent splatter. After clip has bee
n
ecessary for the DSP to find out at what point in time the clip occurred. Based on this information, a
reference level will be set in the Roadrunner. Providing level set in this manner will require at least two SP
activities. The first activity is to read back the timing value "D" from the Sledgehammer IC. The secon
to write the gain setting for the Roadrunner.
B
oth phase and level training are required at least once before transmission of the data in the first slot, but
is not necessarily performed in every transmit slot. DC training will be performed at the start of every
SLOT. All timer values associated with SLOT rising edge will be increased with respect to JANUS
program values to account for the DC training time.
Sledgehammer provides the ability to t
c
lip detector or an external control digital signal V_TERM. V_TERM indicates when the battery current
e
xceeds 3 Amps, which is used to terminate the training ramp to avoid an early radio shutdown during level
tr
aining. Shutdown is avoided by lowering the transmit power when V_TERM is detected. This signal
goes directly to the level set circuitry.
30
n detected, and before the beginning of data, a SPI read is
erminate the level training ramp by either the internal Sledgehammer
cuit to the
º
). The phase shift of the loop
ansmitted,
er IC with the gain set to
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